I'm experiencing this bug since a couple version (some months) hoping it's going to be fixed.
The video thumbnails are made of just horizontal lines, even though they are fine and playable by Mixplorer build in player.
The issue happens to all videos recorded with the stock camera or 3rd party camera apps. Thumbnails of videos from WhatsApp, Instagram or screen recordings are shown correctly though. I tried messaging with codecs and resolutions, with no success to workaround the bug.
I included screenshots and a thumbnail file example from /Android/data/com.mixplorer/cache/thumbs
Here's also one of the bugged videos: https://drive.google.com/file/d/189X...w?usp=drivesdk
It's worth noticing the issue is exclusive to Mixplorer. Video thumbnails are all correct in any gallery like Google Photos or other file managers like the Xiaomi's.
In my case there are only a few thumbs that have these lines, most of them are displayed correct. Almost all video files are made with stock camera.
Sent from my Moto G5 Plus using XDA Labs