Recently upgraded a UniFi-Video VM by creating a new VM and restoring the backup from the previous one. There was a separate virtual disk used for storing all the videos. Although once I reattached it, I had to change the owner to the unifi-video user. lt was reporting that the owner/group was 127 and 134, looks like that was the user ID from the previous VM.
Example output from ls -hla command
drwxr-xr-x 3 127 134 4.0K Jan 16 2020 176de761-8399-3bed-8ceb-917cbe4d25bd drwxr-xr-x 2 127 134 4.0K Sep 10 12:28 21d506ef-dded-31f2-baf8-c109a7e653b9 drwxr-xr-x 4 127 134 4.0K Jan 1 2020 1a3afc4c-a030-39a1-b139-857444c8b71c
Ended up changing the owner to the unifi-video owner with the chown command. /path/to/videos is the mount point of the video drive.
chown -R unifi-video:unifi-video /path/to/videos