zpool's API has some kind of limitation on it. If you poll it too quickly it returns nothing. Thus, appearing down.
If my miner has just polled the API, and then I restart it, 9 times out of 10 the API return is blank. Yes, it's very annoying.
1 query every 10s is the limit.
2018-01-26 11:32:21,345 [ zpool][ pools][ ERROR] zpool API error. Attempt: 1/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:32:32,443 [ zpool][ pools][ ERROR] zpool API error. Attempt: 2/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:37:56,408 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:38:58,324 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:38:58,457 [ zpool][ pools][ ERROR] zpool API error. Attempt: 1/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:39:09,522 [ zpool][ pools][ ERROR] zpool API error. Attempt: 2/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:39:20,585 [ zpool][ pools][ ERROR] zpool API error. Attempt: 3/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:39:31,651 [ zpool][ pools][ ERROR] zpool API error. Attempt: 4/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:39:42,718 [ zpool][ pools][ ERROR] zpool API error. Attempt: 5/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:39:53,803 [ zpool][ pools][ ERROR] zpool API error. Attempt: 6/10. 'ValueError: No JSON object could be decoded'
2018-01-26 11:41:06,678 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:42:08,561 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:43:10,513 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:44:12,434 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:45:14,811 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:46:16,708 [ zpool][ pools][ DEBUG] Getting zpool data.
2018-01-26 11:46:16,888 [ zpool][ pools][ ERROR] zpool API error. Attempt: 1/10. 'ValueError: No JSON object could be decoded'