OK, I’m running a fresh install of Rocketchat on an Ubuntu VM, hosted on an internal private network. Install was from snaps. I’ve set the permissions of the /var/snaps/rocketchat-server/common/* and /tmp/ufs to 777. I’ve restarted the service, I’ve rebooted the VM.
Files stay at 0%. Using GridFS, and it’s not a network issue, because a previous Rocketchat install allowed file uploads.