Comment # 5 on bug 1227111 from Heitor da Silva

Maybe it is not directly related to sleeping or hibernating. 

After around 4 days of usage, during a KDE Plasma session, it started to freeze
the windows and when new ones were opened it just showed the frame of the
window with the title bar, but with no content. When the window was required to
close it didn't respond and the "kill or wait" dialog was showed.

The virtual terminal (TTY) still working normally while Plasma is frozen. I
tried to restart Plasma (systemctl --user restart plasma-plasmashell.service),
but execution timed out.