Thank you for your post.
Apple is aware of this issue, and although it is better with Mac OS X 10.10.3, certain keyboard shortcuts will not be listed in the menus after extended use. Generally, this occurs with Layout mode (Cmd-L), but it can occur with other keyboard shortcuts.
Restarting FileMaker Pro is the recommended workaround at this time.
I have attached your post to the original report. When more information becomes available, I will post again.