Steps to reproduce :

1. Create a new post
2. Create new video block
3. Upload video
4. Create a new block (paragraph/heading ..)
5. Turn off the screen with a power button
6. Turn on the screen with a power button

Result: Last video frame on video block is lost, so it seems that video block is empty, but it isn't as if you click on it, you will see video controls and if you click on the play button, the video will show up.

Video: