I tried to do some mesh paint in new 4.25 editor.
It have a strange behavior for some meshes.
Here is video:As you can see first one is ok. but with next 2 meshes something goes wrong. It tries to mirror or so... Those meshes are overlap and have no collision. I tried to enable it, but no effect. It uses complex collision as simple, maybe that's a problem? But first mesh uses collision settings and it works fine.
I reverted project to 4.24 and with old paint tool everything is ok.
Mesh paint tool worked fine for a many years, why do you need to break it?