Yellow triangle

Something weird is happening with that library.

There are no "Smart Collections" in sight...

When you say "synched" did you mean "relinked"? Or something else?

I would try creating a new library, and dragging the "project" event

to the new library. If asked, allow it to copy everything needed.

Does the new library look normal - including the Smart Collections folder?

You can delete the Smart Collections folder. I have a "helpful" client that does this every time before they hand me a project for some unfathomable reason.

I have two older libraries that have missing media yellow triangles on events and I simply cannot find what's missing. So much so I just gave up on looking for what's missing. I've seen the triangles disappear sometimes after closing and reopening a library.

You might try and dump your cache ship it is forced to rebuilt the filmstrip displays. The project seems to work but the project icon might still be in cache.

I have had this happen on occasion. I recall it eventually clears itself. If not, follow Tom's advice to delete the cache and maybe that will force FCP to see that there are no missing files.