1. After around 20-30 mins of mining, I get a message of No data (in chinese) and it stops mining for about 10 minutes. Then starts up again and continues mining. Wondering whether it's a BT thing...
Could be a network issue, try a different ethernet cable, and also reset the miner and flash the latest firmware, you should also include the kernel for this miner.
2. Of the 3 chains on the reporting page, the first one doesn't appear to have any hashing rate. The asic status is ok and all the other figures. The PCB temp is 51, the chip temp is 71 and the frequency is 555 compared to the other 2 at 585. The fans are all up around 6000rpm.
I suppose the kernel log is for this miner, judging by the temp sensor error on chain 0
1970-01-01 00:17:11 temperature.c:695:get_temp_info: read temp sensor failed: chain = 0, sensor = 0, chip = 55, reg = 1
1970-01-01 00:17:30 temperature.c:695:get_temp_info: read temp sensor failed: chain = 0, sensor = 1, chip = 40, reg = 1
1970-01-01 00:17:50 temperature.c:695:get_temp_info: read temp sensor failed: chain = 0, sensor = 2, chip = 180, reg = 1
1970-01-01 00:17:57 temperature.c:695:get_temp_info: read temp sensor failed: chain = 0, sensor = 3, chip = 195, reg = 0
Each hashboard has 4 PCB sensors labeled 0,1,2,3, after a lot of research, help, and testing we have come to realize that this issue is not caused by the temp sensors themselves but rather bad soldering on one or more of the heatsinks/chips, to fix this you will need to firstly identify the bad chip/heatsink by taking the board out and physically inspect it if there are no signs of anything you will need to use a multimeter like a "fluke" or buy a fixture tool to know which chip/heatsink needs soldering, and then, of course, you will need to have the right sets of tools and skills.
And this is after. The hashrate dropped to zero in this section.
When the miner fails to sense pcb temps from that board, after a certain time it will simply disable it and hash with the two other boards, there is a tiny little chance that by flashing another firmware this board might come back to life, give it a shot but if it doesn't work, you probably want to disconnect it as it does slow the start-up process, also follow the topic posted above by popojeff for more details.