Changes to 3d mesh importer breaking objects

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.

Which breaks everything

Is there any way to disable this “feature”

Cheers

Paul

More information.
Assets created with 5.1 are fine, no problems at all.
However if you move them to the 5.2 project, the meshes are broken.

This is killing me, why has this been implemented?

Correction it is broken in 5.1 as well.

You cannot have multiple material slots if the tris assigned to those material slots are not uniquely applied.

Total rubbish, and for me actually makes UE5 unusable.

I don’t have the money to redo thousands of man hours of TA work.

I am not sure what to do now.

Oh and just a word of caution, don’t go back to 5.1 from 5.2 if you have edited any assets, they will vanish