If you could share the video in some way (e.g. uploading to a file locker) it could be useful.
Are you using a syncing service? If so, are your preferences always offline? I’m not finding it now, but I recall someone with the same issue and it boiled down to a problem with the syncing, in which whatever service (I don’t recall which) was seemingly reverting the relevant file.
After the above, the next step would be resetting syncing to the default location and see if you can reproduce.