I have the exact same problem with sync of video’s. Video sync (and all other type of files) is enabled on both phone and computer. Even tried to disable on phone and computer, restart, enable and then restart. Still didn’t work unfortunately
Mobile: Andriod
Computer: Windows 10 Home
Vault size mobile: ~3.1 gb
Vault size computer: ~1.5 gb
Additional info:
There are 6 video files that I think account for the difference in size of both versions of the vault.
Other ideas have synced before but somehow no videos will sync since a couple of days. Just now tested it with a small videa file of 56.8 MB