Hi all, thanks for the feedback.
I tried adjusting shading rate all the way down but it didn’t resolve the mesh lines issue. After a whole day of trials and errors (resintalling characters and material files) I discovered the culprit is the very first HDR image I used for the IBL sphere. So for whatever reason that particular jpg causes those artifacts. Switching the pics to a few other equally huge 5000x2500 jpgs seem to be fine. So far. Will keep the forum posted just in case others bump into similar issues.