Two different people working on the same Rhino 7 file (at different times of course, not both with same file open at once). When I save the file on my end, we've got a wide range of materials across many different layers (walls, floors, windows, etc.). My colleague opens the file later in Rhino 7, does some editing, saves file, and then later I open the same file. For some reason, most of the many many different materials are set to a single material ("sand pbr" in this case). I've spoken with the other person (also an experienced Rhino user) and asked some basic questions like, "Hey, did you reset all the materials?" answer: "No! Hell no!!"
This has happened now with a couple of different Rhino files that we both work on.
I don't recall this happening when we were both using Rhino 6, but I'm not positive about that.
Couple of screenshots attached showing the layer names and material assignments, before and after.
I've sent "feedback" reports for both versions of the file through the feedback option in Enscape.
The files do have different names because I've asked my colleague to start saving the files with new names so we don't overwrite the file that still has correct material assignments.