Occasionally there'll be a codec issue when uploading 1SE videos to Facebook, Vimeo, or YouTube. Over the years we've addressed most of them but sometimes it will crop up.
In the meantime, here is a super quick fix:
Quick 3 MINUTE Do it yourself fix!!
Download the free App iMovie.
Import your mashed 1SE video
Export at the highest 1080 resolution
Take this new video and upload it to whichever social network you're trying to share on
You can also try uploading the video directly to YouTube through the YouTube Capture App.