Material miniatures not showing in inspector select material window.

I have around 100 materials in the project.
When I want to select a material for the game object in the inspector the “select material” window opens. I can see miniatures for some materials, but others are represented just by grey rectangle:

Before more of them were showing.
Apart from not showing miniatures, everything works perfect for the materials.

Can anyone recommend simple fix?
Its Unity 2021.2.11f1

Maybe custom inspector or something?

Ok I have found the work around for this issue. Inside of Unity I copied the folder where all my materials were.
Now all miniatures showing. Materials are doubled on the list but at least I can see the miniatures.
Any other idea please let me know.