Thank you, I had exactly the same issue, just with the added bonus, that "Unassigned Devices" mounted one of my two disks correctly, but after trying to connect the second one, just e big "reboot" showed up, instead of "mount" and I could not change any relevant settings.
I had ages to figure out, that the issue was, that the system tried to use the same mount point for both devices...
So I had to unmount the working one, rename the second one to a different mountpoint, which I was not able to do before, then remount both. Tadaaaaa...