When I work on a project, I open some source files, then close some, then open another an so on. In such scenario, this menu just stops working (i.e. it does nothing visible to me). I have to kill clangbackend.exe process to make it working again. Then it stops again after a short period of time.
The problem never happens when I switch to old code model (by switching off ClangCodeModel plugin).
The project I have this issue on is large.