The problem doesn't appear if I switch to the "Ray Tracing" rendering mode, but the result is not that good

And the "Scanline" mode works normally too
So the problem only appears in the "PBR" mode

It is not possible to give an exact answer because the details cannot be seen from screenshots alone, but the rendering results may be inaccurate due to problems with calculation accuracy, such as when surfaces overlap.
Try checking the results using the simplest shape possible.

If you cannot find the cause, please send the relevant data to our support.

I've created a new material with the same settings (and textures) and it works now, stops working when I switch back to the old one.

I don't know what causes the problem, but I guess it's fixed for now

(just leaving this here in case somebody else gets this problem)