This ‘fix’ is for those who do not own an N version of windows.
Download Win7DSFilterTweaker from the page
Run and check ‘Media Foundation’ codecs aren’t being overridden
(Specifically x64 and .mp4)
If the box is checked, it’s being overridden - uncheck & save.
No need for codec packs and reversible if it breaks your x264 decoder of choice.
Hope that helps.
Note: My stuck quest proceeded after the video was fixed, no need to restart.