My very helpfully host has send me this:
"The newest Chrome (after version 64) does not handle this broken case, so the video cannot be played anymore. The broken video should be re-encoded using the newest ffmpeg which support SSR or libfdk and the problem will be solved."
So this has nothing to do with Moodle. I tried to play the video in an older Firefox, and it worked fine.
I can see that the issue has been discussed on github here: https://github.com/videojs/videojs-contrib-hls/issues/1329, On another website (forgot which) I saw that some people had similar problems with MP3 files