#missing thumbnail

My video files usually show a thumbnail, but sometime today any new video files I make show the icon and not the thumbnail.

I've checked my settings, they're set to showing the thumbnail and not just the icon.

I've also reset the settings, this has not changed anything.

This happens only with video files, but affects all video file types such as MP4 and MOV.

I'm lost as to what's going on and how to fix it. I use the thumbnail A LOT when finding files with the type of hobby I have, so I really hope someone has an ideas what's going on...