I'm using RS 2019.3, and had no problems using the "create from backup" option with a backup from an IRC5 running RW 6.08.
However, I just got an urgent assignment to support some IRC5s that are running RW 6.04.1027. And the "create from backup" option isn't working on backups from these robots.
I used the "Add-ins" menu to add RW 6.04.01, 6.04.02, 6.04.03, and 6.04.05, but no matter which one I select in the "create station" page, the "Create" button remains grayed-out.
The only other hint I see is that there's an empty drop-down for "PRDM-R00000728-A", but I don't appear to have anything to fill that box. And searching for PRDM in the add-ins window turns up nothing.