Yes maybe a problem with sensor temp ?

Since few days, I have difficulties with my Avalon1246 83T : Hashrate drops, and it reboots often. Problems occur in normal or turbo mode
Previously, It worked without problem.

Here are log and picture.

I could catch a log with SYSTEMSTATU[Work: Out Over Hot, Hash Board: 3 ] error ; but I always see 26° / 66° in the dashboard, not high
https://pastebin.com/uGH0PH9w


It's not an internet provider problem, because just next to it in the same room an other 1246 85T runs perfectly.

Note that fans run at 6500 RPM (whereas on other 1246 85T runs at 3500. Maybe it's ok)




Here a view of minerstat where ou can see it works during hours (days) and then it has problems



Any idea of the problem ?