Found some boards coming back in the logs.
[2016-11-07 17:58:28] Reinit board (cs2)
[2016-11-07 17:58:28] spidev0.0(cs2): Found 20 A2 chips
[2016-11-07 17:58:28] Found chip 1 with 100 active cores
[2016-11-07 17:58:28] Found chip 2 with 100 active cores
[2016-11-07 17:58:28] Found chip 3 with 100 active cores
[2016-11-07 17:58:28] Found chip 4 with 100 active cores
[2016-11-07 17:58:28] Found chip 5 with 100 active cores
[2016-11-07 17:58:28] Found chip 6 with 100 active cores
[2016-11-07 17:58:28] Found chip 7 with 100 active cores
[2016-11-07 17:58:28] Found chip 8 with 100 active cores
[2016-11-07 17:58:28] Found chip 9 with 100 active cores
[2016-11-07 17:58:28] Found chip 10 with 100 active cores
[2016-11-07 17:58:28] Found chip 11 with 100 active cores
[2016-11-07 17:58:28] Found chip 12 with 100 active cores
[2016-11-07 17:58:28] Found chip 13 with 100 active cores
[2016-11-07 17:58:28] Found chip 14 with 100 active cores
[2016-11-07 17:58:28] Found chip 15 with 100 active cores
[2016-11-07 17:58:28] Found chip 16 with 100 active cores
[2016-11-07 17:58:28] Found chip 17 with 100 active cores
[2016-11-07 17:58:28] Found chip 18 with 100 active cores
[2016-11-07 17:58:28] Found chip 19 with 100 active cores
[2016-11-07 17:58:28] Found chip 20 with 100 active cores
[2016-11-07 17:58:28] Found 20 chips with total 2000 active cores
[2016-11-07 17:58:29] Accepted 035b2753 Diff 19.5K/8192 BA2 2 pool 0
[2016-11-07 17:58:29] Accepted 035b2753 Diff 19.5K/8192 BA2 2
[2016-11-07 17:58:29] Accepted 043a50a3 Diff 15.5K/8192 BA2 2 pool 0
[2016-11-07 17:58:29] Accepted 043a50a3 Diff 15.5K/8192 BA2 2
(5s):164.8M (avg):198.8Mh/s | A:1044480 R:0 WU:186784.7/m
[2016-11-07 17:58:30] Accepted 02c6a302 Diff 23.6K/8192 BA2 1 pool 0
[2016-11-07 17:58:30] Accepted 02c6a302 Diff 23.6K/8192 BA2 1
[2016-11-07 17:58:31] Accepted 0634dac1 Diff 10.6K/8192 BA2 1 pool 0
[2016-11-07 17:58:31] Accepted 0634dac1 Diff 10.6K/8192 BA2 1
[2016-11-07 17:58:32] Accepted 01b361ea Diff 38.5K/8192 BA2 0 pool 0
[2016-11-07 17:58:32] Accepted 01b361ea Diff 38.5K/8192 BA2 0
[2016-11-07 17:58:33] chip(cs2) 2: invalid nonce 0xde89c800
[2016-11-07 17:58:33] Accepted 01022d49 Diff 65K/8192 BA2 0 pool 0
[2016-11-07 17:58:33] Accepted 01022d49 Diff 65K/8192 BA2 0
[2016-11-07 17:58:33] Accepted 0732c416 Diff 9.1K/8192 BA2 0 pool 0
[2016-11-07 17:58:33] Accepted 0732c416 Diff 9.1K/8192 BA2 0
[2016-11-07 17:58:33] Network diff set to 30
[2016-11-07 17:58:33] Stratum from pool 0 detected new block
[2016-11-07 17:58:33] Reinit board (cs4)
(5s):173.8M (avg):198.6Mh/s | A:1085440 R:0 WU:191203.8/m
[2016-11-07 17:58:36] spidev0.0(cs4): Found 20 A2 chips
[2016-11-07 17:58:36] Found chip 1 with 98 active cores
[2016-11-07 17:58:36] Found chip 2 with 99 active cores
[2016-11-07 17:58:36] Found chip 3 with 99 active cores
[2016-11-07 17:58:36] Found chip 4 with 99 active cores
[2016-11-07 17:58:36] Found chip 5 with 99 active cores
[2016-11-07 17:58:36] Found chip 6 with 94 active cores
[2016-11-07 17:58:36] Found chip 7 with 99 active cores
[2016-11-07 17:58:36] Found chip 8 with 97 active cores
[2016-11-07 17:58:36] Found chip 9 with 98 active cores
[2016-11-07 17:58:36] Found chip 10 with 99 active cores
[2016-11-07 17:58:36] Found chip 11 with 99 active cores
[2016-11-07 17:58:36] Found chip 12 with 98 active cores
[2016-11-07 17:58:36] Found chip 13 with 98 active cores
[2016-11-07 17:58:36] Found chip 14 with 99 active cores
[2016-11-07 17:58:36] Found chip 15 with 99 active cores
[2016-11-07 17:58:36] Found chip 16 with 95 active cores
[2016-11-07 17:58:36] Found chip 17 with 99 active cores
[2016-11-07 17:58:36] Found chip 18 with 99 active cores
[2016-11-07 17:58:36] Found chip 19 with 99 active cores
[2016-11-07 17:58:36] Found chip 20 with 96 active cores
[2016-11-07 17:58:36] Found 20 chips with total 1962 active cores
[2016-11-07 17:58:38] chip(cs2) 4: invalid nonce 0xa3b1e700
[2016-11-07 17:58:38] Accepted 031d35c4 Diff 21K/8192 BA2 0 pool 0
[2016-11-07 17:58:38] Accepted 031d35c4 Diff 21K/8192 BA2 0
[2016-11-07 17:58:39] Accepted a932e209 Diff 99.2K/8192 BA2 1 pool 0
[2016-11-07 17:58:39] Accepted a932e209 Diff 99.2K/8192 BA2 1
(5s):166.0M (avg):197.9Mh/s | A:1101824 R:0 WU:191204.7/m
[2016-11-07 17:58:43] Network diff set to 30
[2016-11-07 17:58:43] Stratum from pool 0 detected new block
[2016-11-07 17:58:43] chip(cs2) 6: invalid nonce 0x58101100
[2016-11-07 17:58:43] Accepted b975d9b3 Diff 90.5K/8192 BA2 1 pool 0
[2016-11-07 17:58:43] Accepted b975d9b3 Diff 90.5K/8192 BA2 1
(5s):179.0M (avg):198.0Mh/s | A:1110016 R:0 WU:189877.7/m
[2016-11-07 17:58:45] Accepted 04e5d190 Diff 13.4K/8192 BA2 2 pool 0
[2016-11-07 17:58:45] Accepted 04e5d190 Diff 13.4K/8192 BA2 2
[2016-11-07 17:58:47] Accepted 0415b023 Diff 16K/8192 BA2 2 pool 0
[2016-11-07 17:58:47] Accepted 0415b023 Diff 16K/8192 BA2 2
[2016-11-07 17:58:48] Network diff set to 30
[2016-11-07 17:58:48] Stratum from pool 0 detected new block
[2016-11-07 17:58:49] Accepted 05f22e16 Diff 11K/8192 BA2 1 pool 0
[2016-11-07 17:58:49] Accepted 05f22e16 Diff 11K/8192 BA2 1
[2016-11-07 17:58:49] Accepted 0184cebe Diff 43.1K/8192 BA2 0 pool 0
[2016-11-07 17:58:49] Accepted 0184cebe Diff 43.1K/8192 BA2 0
(5s):184.2M (avg):197.9Mh/s | A:1142784 R:0 WU:192635.9/m
[2016-11-07 17:58:52] Accepted 069f0389 Diff 9.9K/8192 BA2 1 pool 0
[2016-11-07 17:58:52] Accepted 069f0389 Diff 9.9K/8192 BA2 1
[2016-11-07 17:58:52] Accepted 068856c6 Diff 10K/8192 BA2 1 pool 0
[2016-11-07 17:58:52] Accepted 068856c6 Diff 10K/8192 BA2 1
[2016-11-07 17:58:53] Network diff set to 30
[2016-11-07 17:58:53] Stratum from pool 0 detected new block
[2016-11-07 17:58:53] Reinit board (cs4)
[2016-11-07 17:58:53] spidev0.0(cs4): Found 20 A2 chips
[2016-11-07 17:58:53] Found chip 1 with 98 active cores
[2016-11-07 17:58:53] Found chip 2 with 99 active cores
[2016-11-07 17:58:53] Found chip 3 with 99 active cores
[2016-11-07 17:58:53] Found chip 4 with 99 active cores
[2016-11-07 17:58:53] Found chip 5 with 99 active cores
[2016-11-07 17:58:53] Found chip 6 with 94 active cores
[2016-11-07 17:58:53] Found chip 7 with 99 active cores
[2016-11-07 17:58:53] Found chip 8 with 97 active cores
[2016-11-07 17:58:53] Found chip 9 with 98 active cores
[2016-11-07 17:58:53] Found chip 10 with 99 active cores
[2016-11-07 17:58:53] Found chip 11 with 99 active cores
[2016-11-07 17:58:53] Found chip 12 with 98 active cores
[2016-11-07 17:58:53] Found chip 13 with 98 active cores
[2016-11-07 17:58:53] Found chip 14 with 99 active cores
[2016-11-07 17:58:53] Found chip 15 with 99 active cores
[2016-11-07 17:58:53] Found chip 16 with 95 active cores
[2016-11-07 17:58:53] Found chip 17 with 99 active cores
[2016-11-07 17:58:53] Found chip 18 with 99 active cores
[2016-11-07 17:58:53] Found chip 19 with 99 active cores
[2016-11-07 17:58:53] Found chip 20 with 96 active cores
[2016-11-07 17:58:53] Found 20 chips with total 1962 active cores
[2016-11-07 17:58:54] Accepted 84bc37cd Diff 126K/8192 BA2 1 pool 0
[2016-11-07 17:58:54] Accepted 84bc37cd Diff 126K/8192 BA2 1
(5s):182.2M (avg):197.6Mh/s | A:1167360 R:0 WU:194008.0/m
[2016-11-07 17:58:56] Accepted 0460fb42 Diff 15K/8192 BA2 0 pool 0
[2016-11-07 17:58:56] Accepted 0460fb42 Diff 15K/8192 BA2 0
[2016-11-07 17:58:56] Accepted 07cc8ef2 Diff 8.4K/8192 BA2 1 pool 0
[2016-11-07 17:58:56] Accepted 07cc8ef2 Diff 8.4K/8192 BA2 1
[2016-11-07 17:58:58] Accepted 04dcbee1 Diff 13.5K/8192 BA2 1 pool 0
[2016-11-07 17:58:58] Accepted 04dcbee1 Diff 13.5K/8192 BA2 1
[2016-11-07 17:58:58] Stratum from pool 0 detected new block
(5s):188.3M (avg):197.6Mh/s | A:1191936 R:0 WU:195378.5/m
[2016-11-07 17:59:01] Accepted 07cfab3d Diff 8.39K/8192 BA2 0 pool 0
[2016-11-07 17:59:01] Accepted 07cfab3d Diff 8.39K/8192 BA2 0
[2016-11-07 17:59:02] chip(cs2) 19: invalid nonce 0x0270aa00
[2016-11-07 17:59:02] Accepted 016f76fe Diff 45.7K/8192 BA2 1 pool 0
[2016-11-07 17:59:02] Accepted 016f76fe Diff 45.7K/8192 BA2 1
[2016-11-07 17:59:03] chip(cs3) 5: invalid nonce 0xc398ff00
(5s):193.6M (avg):197.7Mh/s | A:1208320 R:0 WU:195324.8/m
[2016-11-07 17:59:06] Accepted 0482a875 Diff 14.5K/8192 BA2 2 pool 0
[2016-11-07 17:59:06] Accepted 0482a875 Diff 14.5K/8192 BA2 2
[2016-11-07 17:59:08] Accepted 0247e1b6 Diff 28.7K/8192 BA2 2 pool 0
[2016-11-07 17:59:08] Accepted 0247e1b6 Diff 28.7K/8192 BA2 2
[2016-11-07 17:59:09] Accepted 02972cfb Diff 25.3K/8192 BA2 1 pool 0
[2016-11-07 17:59:09] Accepted 02972cfb Diff 25.3K/8192 BA2 1
(5s):198.4M (avg):197.8Mh/s | A:1232896 R:0 WU:196594.3/m
[2016-11-07 17:59:11] Accepted 0300ab90 Diff 21.8K/8192 BA2 1 pool 0
[2016-11-07 17:59:11] Accepted 0300ab90 Diff 21.8K/8192 BA2 1
[2016-11-07 17:59:11] Accepted 1b1bd072 Diff 619K/8192 BA2 2 pool 0
[2016-11-07 17:59:11] Accepted 1b1bd072 Diff 619K/8192 BA2 2
[2016-11-07 17:59:11] chip(cs4) 17: invalid nonce 0x3d868d02
[2016-11-07 17:59:11] Accepted 441acffe Diff 246K/8192 BA2 0 pool 0
[2016-11-07 17:59:11] Accepted 441acffe Diff 246K/8192 BA2 0
(5s):200.6M (avg):197.9Mh/s | A:1257472 R:0 WU:197881.9/m
[2016-11-07 17:59:15] Accepted 070840b1 Diff 9.32K/8192 BA2 1 pool 0
[2016-11-07 17:59:15] Accepted 070840b1 Diff 9.32K/8192 BA2 1
[2016-11-07 17:59:19] chip(cs3) 9: invalid nonce 0xb2045104
(5s):202.9M (avg):198.0Mh/s | A:1265664 R:0 WU:196552.0/m
[2016-11-07 17:59:20] Network diff set to 30
[2016-11-07 17:59:20] Stratum from pool 0 detected new block
[2016-11-07 17:59:21] Accepted 0160d952 Diff 47.5K/8192 BA2 1 pool 0
[2016-11-07 17:59:21] Accepted 0160d952 Diff 47.5K/8192 BA2 1
[2016-11-07 17:59:21] chip(cs2) 5: invalid nonce 0x6bbc2300
[2016-11-07 17:59:22] chip(cs2) 6: invalid nonce 0x34e93d00
[2016-11-07 17:59:23] Accepted 05ff3750 Diff 10.9K/8192 BA2 0 pool 0
[2016-11-07 17:59:23] Accepted 05ff3750 Diff 10.9K/8192 BA2 0
[2016-11-07 17:59:24] Accepted 02f03bd2 Diff 22.3K/8192 BA2 2 pool 0
[2016-11-07 17:59:24] Accepted 02f03bd2 Diff 22.3K/8192 BA2 2
[2016-11-07 17:59:25] chip(cs3) 13: invalid nonce 0x0bffc800
(5s):201.2M (avg):198.0Mh/s | A:1290240 R:0 WU:197764.5/m
[2016-11-07 17:59:26] Network diff set to 30
[2016-11-07 17:59:26] Stratum from pool 0 detected new block
[2016-11-07 17:59:28] chip(cs4) 19: invalid nonce 0x5be24900
[2016-11-07 17:59:28] Accepted 01b369e2 Diff 38.5K/8192 BA2 0 pool 0
[2016-11-07 17:59:28] Accepted 01b369e2 Diff 38.5K/8192 BA2 0
[2016-11-07 17:59:30] chip(cs2) 17: invalid nonce 0xfd889f00
[2016-11-07 17:59:30] Network diff set to 30
[2016-11-07 17:59:30] Stratum from pool 0 detected new block
[2016-11-07 17:59:30] Reinit board (cs3)
[2016-11-07 17:59:30] spidev0.0(cs3): Found 20 A2 chips
[2016-11-07 17:59:30] Found chip 1 with 100 active cores
[2016-11-07 17:59:30] Found chip 2 with 100 active cores
[2016-11-07 17:59:30] Found chip 3 with 100 active cores
[2016-11-07 17:59:30] Found chip 4 with 100 active cores
[2016-11-07 17:59:30] Found chip 5 with 100 active cores
[2016-11-07 17:59:30] Found chip 6 with 100 active cores
[2016-11-07 17:59:30] Found chip 7 with 100 active cores
[2016-11-07 17:59:30] Found chip 8 with 100 active cores
[2016-11-07 17:59:30] Found chip 9 with 100 active cores
[2016-11-07 17:59:30] Found chip 10 with 100 active cores
[2016-11-07 17:59:30] Found chip 11 with 100 active cores
[2016-11-07 17:59:30] Found chip 12 with 100 active cores
[2016-11-07 17:59:30] Found chip 13 with 100 active cores
[2016-11-07 17:59:30] Found chip 14 with 100 active cores
[2016-11-07 17:59:30] Found chip 15 with 100 active cores
[2016-11-07 17:59:30] Found chip 16 with 100 active cores
[2016-11-07 17:59:30] Found chip 17 with 100 active cores
[2016-11-07 17:59:30] Found chip 18 with 100 active cores
[2016-11-07 17:59:30] Found chip 19 with 100 active cores
[2016-11-07 17:59:30] Found chip 20 with 100 active cores
[2016-11-07 17:59:30] Found 20 chips with total 2000 active cores
(5s):197.3M (avg):197.9Mh/s | A:1298432 R:0 WU:196467.2/m
[2016-11-07 17:59:31] Network diff set to 30
[2016-11-07 17:59:31] Stratum from pool 0 detected new block
[2016-11-07 17:59:32] Accepted 01d711ec Diff 35.6K/8192 BA2 0 pool 0
[2016-11-07 17:59:32] Accepted 01d711ec Diff 35.6K/8192 BA2 0
[2016-11-07 17:59:33] Accepted 07e5aba0 Diff 8.3K/8192 BA2 1 pool 0
[2016-11-07 17:59:33] Accepted 07e5aba0 Diff 8.3K/8192 BA2 1
[2016-11-07 17:59:34] chip(cs2) 19: invalid nonce 0x1e7f8f00
(5s):190.4M (avg):197.7Mh/s | A:1314816 R:0 WU:196467.8/m
[2016-11-07 17:59:37] Accepted 0164c98e Diff 47K/8192 BA2 2 pool 0
[2016-11-07 17:59:37] Accepted 0164c98e Diff 47K/8192 BA2 2
[2016-11-07 17:59:38] Accepted 01f796f9 Diff 33.3K/8192 BA2 1 pool 0
[2016-11-07 17:59:38] Accepted 01f796f9 Diff 33.3K/8192 BA2 1
[2016-11-07 17:59:39] Accepted 070edd9f Diff 9.29K/8192 BA2 0 pool 0
[2016-11-07 17:59:39] Accepted 070edd9f Diff 9.29K/8192 BA2 0
[2016-11-07 17:59:39] chip(cs4) 19: invalid nonce 0x8cbd6701
[2016-11-07 17:59:40] Accepted 0205216c Diff 32.4K/8192 BA2 0 pool 0
[2016-11-07 17:59:40] Accepted 0205216c Diff 32.4K/8192 BA2 0
(5s):195.4M (avg):197.7Mh/s | A:1347584 R:0 WU:198838.6/m
[2016-11-07 17:59:43] Accepted 04c61240 Diff 13.7K/8192 BA2 1 pool 0
[2016-11-07 17:59:43] Accepted 04c61240 Diff 13.7K/8192 BA2 1
(5s):198.5M (avg):197.8Mh/s | A:1355776 R:0 WU:197557.3/m
[2016-11-07 17:59:46] chip(cs4) 19: invalid nonce 0x9cd5cd02
[2016-11-07 17:59:46] chip(cs2) 6: invalid nonce 0x5066fc02
[2016-11-07 17:59:48] Shutdown signal received.
I also hope this is a software problem.
Is it possible that communication between the boards and the raspberry is terrible(or wrong configuration) and causes the board to drop?