For users with artefact issues in fullscreen:
This bug might be linked with this one:
I noticed that when my macbook plays a video through netflix, the black level/contrast just become much brighter when the playback menu is on / or if subtitles is on.
Anyone with the similar bug?
If this is the case then I think that this might be the reason why when you hover on the video; the playback menu will come up and flux won't produce the artefact.