I have the same issue.
If I know and use the remote ip everything works great with the remote backup. But from time to time the remote ip changes, so I have a ddns account for that reason. The problem is on the remote settings of the “remote backup” application. It allows you to enter ONLY the remote ip and not the ddns url (that points to the remote ip).
For the time being I check and update the remote ip manually, but it would be much easier to be able to put the ddns url at the remote ip field.
I have 320L and 327L and this happens on both machines, so the issue is at the “remote backup” application…