Square artifacts in rendered sequence movie

so there are these hefty artifacts when rendering a sequence to a movie. tested with compression and without…both the same.
resolution is 1920x1080
any clue what goes on there? i never experienced these errors. but today i installed a second screen. could this be the reason? i’ll test this later by reve
rting my setup. but when you have other ideas i’d be glad to hear them.

k. turns out i had to turn it off and on again *madlaughter…
a pc restart is still a thing these days. all the footage was actually working but only displayed wrong.