this is a rough one without looking at the assets. My approach would be to simplify everything by removing a peice on at a time.
Simplify the material a step at a time. Remove refraction, then plug simple roughness constant, then simple color constant, etc.
Then if still visible remove each post process one at a time.
Once you find the things that exacerbate the issue then you can have info on reproducing it easily for others to help test.