I get some blurry artifacts on a glass shader in my very simple setup (see image1).
2 meshes, smoothed with SubD (2) modifier : glass container on the outside (mesh1, image2), coffee or other liquid in the inside (mesh2, image3).
Principled BDSF on both meshes.IOR around 1.3-1.4 and transmission near to 1 (0.99).Normals are ok. Meshes are overlapping.
Lightning : world (white, strength : 1.5)
When mesh2 is outside from mesh1, problem seems to disappear.
Level of SubD has no effect on the artifact.
When i rotate the view around the object, artifacts stay at the same place.
When i modify the IOR of the glass shader, artifacts become bigger or smaller.
So, what could it be ?