- Model geometry objects should not have overlapped UVs across the same UV island.
- Different UV islands can be overlapped with each other if it is needed:
- to place all UV sets into [0-1] UV area.
- to stack similar UV islands (for optimization purposes).
How to solve
- Make sure that UV seams are made correctly.
- Try to avoid having concave UV polygons, in some cases it might cause UV overlaps.
- Try to Unfold/Relax selected UV islands or move UV vertices manually.