Why did my materials turn pink in the project view?

Somehow some of my materials turn pink in the project view. They look normal in the inspector. Can anyone explain to me why?

Best regards,
Max

hey;
try Assets > ReimportAll

this may take some time depend on your project size and have a back up too ;

I haven’t been able to find a solution, so any hint would be useful!

It could be that the reference to the texture or shader is missing. As far as I see, the texture is there. If you wrote the shader outside of unity, you need to import it into unity so it has a reference.