mpv, mplayer, vlc, and OpenGL applicaitons like Kodi. Fury Nano.
Erratic flickering, usually when an OpenGL application is started on the non primary monitor or moved between nonprimary and primary. Entire frames will not be filled in occasionally as if it was just dropped from the render queue for up to maybe 4 or 5 frames.
Non OpenGL backends not having as many problems.
I've also occupationally noticed massive slowdown unrecoverable screen corruption when unplugging / plugging back in a monitor when I was finalizing my setup. These likely have different but related origins but geh, the driver needs more polishing on robust/recovery.