I think that you can isolate the issue.
1. Back up to your local disk. If the issue is gone, the cause is in NAS side.
2. Do the backups for volume. If the issue is gone, the cause is in files and folders backups.
3. Select the other files or folders when creating files and folders backup job, and do the backups.
If the issue is gone, the cause is specific files or folders. Please run CHKDSK command.
4. In general, when the backup job hangs up at 5%, shadow copy process is running.
The shadow copy is created by VSS on the OS. So try to back up after Windows Update.
1. I will backup to the local drive and report back on this.
2. It only happens when creating files and folders backups.
3. It does it on all files and folder backups.
4. Windows updates are not running at the time of backup. But since it is always 5%.. and it is, maybe it has something to do with it.
