[opensuse-factory] Snapper: cannot boot from any snapshots

Hi I am unable to boot from any snapshot. After selecting the option to boot from a read-only snapshot, and then selecting a snapshot, I see a message that says something like "if OK, run snapper rollback and reboot" but I can't do anything from there. Pressing enter refreshes the screen and I see the same message. I can enter the GRUB menu and such, I just can't actually boot. Obviously this is quite alarming as I'd always thought I can rely on Snapper and is one of the reasons I'm happy to use Tumbleweed. Any suggestions? Kind regards, Huw