I installed Debian/Dietpi alongside Windows/Lubuntu on an older PC, been running great.
But today I did the update to v9.12.1 and now it won’t boot with this error message:
error: file ‘/boot/vmlinuz-6.1.0.32-amd64’ not found.
error: you need to load the kernel first.
Press any key to continue…
I see ‘/boot/vmlinuz-6.1.0.33-amd64’ but not .32, any suggestions?
Thanks.
More info:
Debian/Dietpi is installed on a second SSD and I see grub.cfg on this drive is indeed pointing to ‘/boot/vmlinuz-6.1.0-33-amd64’
but grub.cfg on the first drive is pointing to ‘/boot/vmlinuz-6.1.0-32-amd64’
So I ran ‘update-grub’ and the issue is fixed, but now I gotta figure out how to get the second drive to use grub on the first drive.
Hmm, so both systems currently use the same GRUB config but a different kernel? 
How are thinks partitioned/mounted?
Normally I would suggest /boot/grub/grub.cfg and /boot/vmlinuz-* to be on the same drive/partition used as root by one OS an hence both always kept in sync.
… ah but wait, the OS list to pick from at boot can be on any first drive picked by the GRUB binary. Is GRUB managed by both, DietPi and Ubuntu, and they use os-prober or so to add boot menu entries for each other?