I know about the feature where material auto-delete itself with 0 users. But I got materials without any user (I checked manually all objects) and they do not have fake user, but still they have some invisible fake user or something.
How to fix it?
Do you have linked files in the scene? Or appended things?
I had this a couple of times, and it ended up being old links that ‘stuck’ in the scene after making everything local.
maybe it helps,
rob
edit: Be sure to activate the ‘Material Utilities’ add-on in Blender.
It does what you want for the shared materials search, but it also makes assigning shaders a smoother workflow. Especially for ex-Maya users it looks familiar at least