Just swapped over to 5.2 and found all my objects are broken.
The reason is the asset importer.
I use wavefront obj files and the design is to use as few polygons as possible, so we use overlays.
So a tri on the mesh may be included in draw lists with multiple textures.
For example the tail of an aircraft will have the base texture applied to all tris.
Then some tris will have a texture applied on top of this with the aircraft identity numbers , the country roundel, the squadron number , etc.
With the new importer all the tris have a single material applied to them , the last in the list.