Tried after converting both to mp4 (with Compressor) and they show as video in the post preview before posting, but after posting just show as an icon.
So I think this is mostly the same as this report, which I've just fixed: https://xenforo.com/community/threads/insert-video-post-2-time.156631/ The issue was that they weren't being embedded as expected when inserted through the video insert menu. I'm going to tag this as a duplicate for now, but if you can still reproduce any issues here let us know. I am curious about that m4v video that triggered that "something went wrong" error, though it could have been specific to the configuration at the time (as we now have distinct video attachment limits).