When looking at a painting in a certain angle while right next to it, it disappears.

This is a vanilla bug and happens with Armorstands/Players/many other bigger entities too. To test rather something is caused by the culling mod you can bind a toggle in the controlls. If it shows up/vanishes when pressing this toggle, then it's a bug of the mod.

Edit: after testing around for a bit I did manage to replicate it, I assumed you meant camera angle and not angle to the painting. I'll look into it.

Also occasionally happens with item frames.

Fixed in the newest release, this took way too long to debug :/