non-interactive upgrades get stuck (loop) on warn/fail prompts

After a test installation was off for several days I've triggered a manual update, but it seems it got stuck.

Even shortly after forcing a reboot the upgrade is still in progress, this was sticking out from the process list:

/usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/grub-pc.postinst configure 2.04-12

After terminating the related processes, I could manually run dpkg --configure -a and after answering the interactive frontends grub install device question everything finished without errors.

Only thing suspicious to me was that the default target device name (sda) apparently now pointed to a device that was not the root. (Device names seem to got switched after a reboot, which can happen.)

I guess the upgrades run in non-interactive mode, but are problems supposed to be shown to the user in plinth?

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From discussion below:

More generally though, couldn't plinth notice and show errors and provide an interrupt button in this case? (Then recommend the proper manual interactive commands.)