I know this unreal forum but it seems like you guys know everything about blender so I am posting.
I have made this asset tha has 3 seperate uv mappings for the blue,red and green mesh. I have also added a diferrent material for each of them.
My problem is that it is supposed to be one mesh and when I join them the materials get mixed (the red has become blue in some parts) I have tries it using both join and boolean and the result is the same.
Some other meshes I have used this method before are fine and other have this same problem. Any solution?