All shaders disappeared


I just had an issue, I’ve never seen that before:
I’ve been working for a long time on a maya scene. Just modeling, with simple blinn shaders.
Today, I opened the scene as always but then surprise, all the shaders have disappeared. There’s nothing in the hypershade, and of course, all my meshes have gone green.
Also, one mesh disappeared, and another got all fucked up.
There is a reference in the scene that is ok though, it still has its shaders.
I had duplicated some of those shaders to add the same color to my non-reference meshes. When I try to do it again, (assign duplicated shader to a mesh), i have an error message : “No object matches name: internal_standInSE.”
It’s ok when I create a new shader and assign it, though. I understand the duplicated shader might not be a good option, but I don’t know why it perfectly worked before…
I must admit, yes, on a few meshes, I had several shaders applied to faces… I shouldn’t have, but it worked…

Also, the color management reactivated (whereas I had deactivated it), and I had a display layer that also disappeared.

So, my question is: is there a simple way to recover my shaders, or do I have to create and assign them all again? Does someone know where this problem came from, and how to avoid it in the future?
Thank you in advance!

Ps: Maya 2019 (.ma scene), windows 10


just apply the shaders again.