Shared material libraries assets along with textures of appearance and images are notoriously troublesome in Revit, especially if you have multiple remote users using BIM 360. I am not aware of a work around or solution for custom materials. If a material library links to custom images (even when within a shared cloud image library) in one location (c:user\user1\BIM360..) and then opens the project in another location (c:user\user2\BIM 360..) all of the appearance images links break. Adding "additional render appearance paths" via the options panel does not correct the broken links. It is unclear to me the purpose of this optional function. Instead, each material path needs to be relinked which is almost an impossible task without knowing which material assets need the corresponding missing images. When rendering, Revit error message indicated what image links are broken but this information is insufficient to help correct problem, but at best it is a tedious process and a never ending problem.
The solution would be to let users add "additional rendering appearance paths" for missing appearance images, thus automatically relink missing images.
