When importing a file from Blender, UE creates the correct number of materials, but the number of textures is incorrect and is being overwritten, and not importing the correct amount.
Tested and reproduced in 4.25.3 (13942748) and 4.24.3 (11590370)
1. Create a New project
2. Create a model (I used blender) with material slots having textures assigned with the same name and export FBX.
3. Import in UE4 using create materials create instanced materials (bug may also be present in create materials), set material properties as in parent material (diffuse etc) and import.
UE4 creates correct number of materials but wrong number of textures (apparently if texture name is same it does not get imported). Also random textures (from imported file (which does not come under the condition of same name)) gets assigned to the material.
The duplicate name textures should be renamed and exported. i.e if material slot named "Material1" has a texture named "Material1" it should rename texture to "Material1.Tex.00x" and continue importing it.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-96228 in the post.