Hello Heimir, 

In Build 6911 (Dec 2018), we added the ability to enable/disable users' ability to automatically forward messages per domain and per user. If the User Defaults setting for "Forward all email to another address" is enabled, then this is what Admins will see when they view a user who has the ability to use automated forwarding. If the Forwarding Address is blank, it indicates they haven't set on up. 

On the user end, they'll see the card like this: 

If you find any indication that a forwarding address was lost on upgrade, please provide us details in a support ticket so we may investigate further. However, since this change in 2018, we are not aware of any bugs or reports of forwarding addresses being lost on upgrade. 

I hope this helps!