Trying out the 5.6a beta right now on a 8 x 3090 rack. After 8 hours in and it seems like the stale rate has dropped a bit and hashrate seems a tad more stable on the pool end.
A bit early to say 100% success but so far 0 issues...
I have the same issue with my 3080’s . My 1070’s are performing very well
Seems to be a problem with the 30 series and would be nice if Phoenixminer devs would address this and see if maybe its something they can tweak in their software .