It seems that the fan is not automatically running at high speed after the hash board reaches its temp limit.
Would you mind to try aging to calibrate the miner?
Use the FMS tool to aging the miner you can download the tool here
https://canaan.io/service/447There is 3 FMS tool only one has an aging button so download the 2nd or I think the 3rd one from that link.
If you start the aging process without 3 good hash boards then it will be stuck in aging-mode until you fix the hash boards. All versions of FMS have the command line tool: click the diagnose button.