warming up is not a case, last time started happening at 5 am, when cards are usually coldest. even during the day, cards run at 45c with fan 21%, 21% is minimum fans can spin
Also tried changing clocks, didnt helped. Running for 6 months on phoenix with same clocks and no problems before this
I had a sort of similar issue and i found 1 card had tilted slightly in its riser. I went and resat all cards and things went back to normal.