Do I understand correctly that this happens every time you click away to another application then back to ArchiCAD? If so, that's rather strange. What probably happens is that there is a library reference that ArchiCAD tries to resolve, therefore tries to mount the server, but since the case sensitive thing the mounted volume is not what ArchiCAD is looking for.
Try signing in as team leader with exclusive access from a Mac, clear up the Library Manager (delete missing libraries, fix loaded libraries) then do a send and receive. Does it help?
Gergely Kmethy
VP, Customer Success, Graphisoft