Material problem when convert project

Hello, I want to change my project from 4.21 to 4.26. I realise that some of my texture disapear.The first picture is in 4.21 and the next one is 4.26.

If you noticed there is a section who is missing, and i do some research and I don’t think I can add a section to a static mesh.
I also try to convert my projet to 4.21 to 4.22 and i have the same problem.
This problem is in every mesh that I created with more than 1 Material.
Tell me if it does the same thing with your projet.