This has occurred several times now. I will have an Emacs session (24.5.1, OSX UI version installed via homebrew) running for a while when suddenly it no longer seems to understand how to navigate between visible windows.
other_windowwill switch from left-most to right-most window, but not back
windmove-rightwill work but
windmove-leftwill say "No window left from selected window" when obviously there is
Mouse-clicking in a visible window works fine.
Any ideas what is going on? I see no other error messages displayed anywhere. Restarting emacs restores correct behavior until it breaks again later.