The root cause is not MC or JRVR or video drivers. The root cause is Windows hot plug detect, search google for "hot plug detect Pin 19". This mostly affects dual monitors / extended desktop setups.
Basically when Windows detects that one of the connected "monitors" changes resolution, or is shut off, or the input changes etc, Windows "moves/resizes" any full screen apps/video, and even desktop icons, into the top left corner of the screen. Watch the following video:
https://www.youtube.com/watch?v=5Y3jnk5g4UIThe fix is to trick Windows into thinking that the dual monitor / extended desktop configuration stays constant. Some GPU's have EDID override to get around this, like nvidia Quadro or some newer Intel NUC's. But if your GPU does not, the BEST way to trick Windows is an external hdmi hardware EDID device. I tried many - several active hdmi switches, "monitor detect killer" (pin 19), 4k HD Fury, but the only one that provides ZERO problems ended up being:
https://atlona.com/product/at-etu-sync/