Nerdzmasterz about "not visible" thing, I also experienced once.
What I did was try to delete the MeshLibrary and re-export one. Though what really worked is re-export and replace the old file (not deleted manually) with an option on (My godot is languaged Chinese, I think it might be "replace" or "keep" or "adding" thing?... in the exporing(?to MeshLibrary) window)
