[SOLVED] Custom shader Drag & Drop, won't apply to objects.

Hello,
My material with custom shader won't apply to objects when dragging, but apply to the skybox.
Red is Standard Shader, Yellow is Amplify custom Shader

I can drag materials to the deserved slots of the Mesh Renderer, this works fine, but I have a lot of materials IDs on my models, so it is very tedious to do. Also, since i'm working on a pack that will be sold on the Asset Store, I definitively can't let this through.
I have asked on Unity forums, Unity answers, Reddit, no responses.
Is there any reason or solution to this ? I can't seems to find notable differences between a skybox and a surface shader.
My material with custom shader won't apply to objects when dragging, but apply to the skybox.
Red is Standard Shader, Yellow is Amplify custom Shader

I can drag materials to the deserved slots of the Mesh Renderer, this works fine, but I have a lot of materials IDs on my models, so it is very tedious to do. Also, since i'm working on a pack that will be sold on the Asset Store, I definitively can't let this through.
I have asked on Unity forums, Unity answers, Reddit, no responses.
Is there any reason or solution to this ? I can't seems to find notable differences between a skybox and a surface shader.