I've noticed a strange artifact that happens under three conditions:
- All the edges of a mesh have at least minimum Edge Crease to them.
- There's a Bevel modifier with non-zero width (it has to actually modify the geometry)
- There's a Subsurf modifier (Catmull-Clark, at least 1 Subdivision) after the Bevel
The artifact seems to appear on certain border edges, it can be removed by setting the Edge Crease to 0 for that particular edge:
Here all edges have full Edge Crease:
Here the problematic edges have Edge Crease of zero:
I attach a test .blend file: