Windows 10: MP4s lose thumbnails, but gain icons; AVIs still have thumbnails.

Something happened to my HDD today causing MP4s to lose their thumbnails, but a clone that was made a few days ago, first shows generic icons for the default Player, then after a moment, they turn into thumbnails. I'd like to understand what is going on, and above all, how to make the non-clone show thumbnails again for MP4s.

:)

 

Can't see AVI video thumbnails

As the title says, I can view MP4 thumbnails, but not AVI.

 

.mp4 thumbnail icons!?

Did the feature update this morning and now I don't get thumbnail previews for .mp4 files only!

Any idea why anyone!? I like my thumbnails!!!

Chuter.

EDIT: To be more specific it seems it's only not going to show me the .mp4 video thumbnails for the videos that came from my MotoZ2 play device which are in 4k. if that may have anything to do with it?

 

Thumbnails for Video Files (such as mp4) Are Not Working

Within the last couple of days, thumbnails for video files (particularly mp4) seem to have stopped appearing. New files would not get thumbnails, while thumbnails for older files remained. Even more odd, these new mp4 files would receive thumbnails while
being uploaded to OneDrive, but would lose their thumbnails after uploading / syncing was complete.

Recently, I cleared my thumbnail cache using Disk Cleanup, but that did not fix the issue. Instead, I lost all of my thumbnails, including the ones that remained for the older mp4 files (I have done the obvious as well, such as refreshing my Windows Explorer
session following disk cleanup and even rebooting). So, I tried clearing the thumbnail cache again using an administrative command prompt, and I got the same result.

Is there any way to fix this problem? Thanks in advance.