I'm not exactly sure what might cause the IDE to enter this abnormal state. In this state, all files are opened with no content. Every opened file is blank. It really scared me the first time I encountered this, thinking "Oh no, all my work is gone!" :) However, closing down the project and restarting the IDE would reset the abnormal state. The files still have their contents. I'm not sure about unsaved files though.

When closing these blank files, we see this
log message,

IDEEditor I Cannot notify language server. File is null. 

This bug is not that rare. Just actively close and open files and it'll happen.