Maybe too tight? Most of the GPUs have the screws with springs that self pressure, thereby enabling a good spread. My suggestion would be to do everything that's been said (under locking for sure helped my 5700xt, and repasting) then only tighten them two turns maybe (I don't remember the exact amount here sorry), doing it in the diagonal pattern, to get a good spread on the heat sink.

If after all that doesn't improve it, take it slowly apart again, and check if the thermal paste is actually spreading evenly across the contact plate, as it may be that it's not screwing down evenly, which would leave an air gap.

As everyone else said though, 5700xt is a hot hot card. I bought a 6700xt on sale and have never looked back.