I'm not sure if this is the best way to fix this, but the cinema manager code in rP19375 (or maybe earlier, I'm not sure) broke the hotkeys that toggle unit silhouettes (default "Alt+S"), and the visibility of session GUI (default "Alt+G") (mentioned by @Imarok in D548). This is because CinemaManager.Update is called constantly in Update in GameView.cpp, even though currently the CinemaManager is not used often, and in any case, it seems it only needs to be updated when it is actually playing (in Atlas it's handled differently). Whenever Update is called, the CinemaManager calls two functions that set the visibility of session GUI and sets the config option for unit silhouettes, which prevents the hotkeys from working.
(Notice that before rP19375 CinemaManager.Update would only be called if it was actually enabled, so this diff does that.)
Another option might be to do the check (if the CinemaManager is actually enabled) directly in CCinemaManager::Update.