I've just started running El Capitan (10.11.5) and one of my favorite keyboard shortcuts seems to have disappeared: the keyboard shortcut that let you move between windows within the same application. It used to be <kbd> Cmd ⌘ </kbd> <kbd> ` </kbd>  (tilde) but now that shortcut doesn't work and I can't figure out how to get it back. 

Any ideas? Thank you in advance.