I was getting an annoying "failed to update metadata for lvfs" in the Kubuntu 'discover' app. This was causing no problems, but I found a site that recommended fixing it by running fwupdmgr --force refresh
After doing that, the system rebooted on the next attempt to install updates - and would either reboot or just hang the updater any time I tried to update. So, figuring I had somehow installed a bad package on my system, and because I was running 20.04, I decided to move forward and install 22.04.1, which seemed to have fixed it (i.e., I was able to perform updates again). But the latest updates caused the crash again. I noticed that one of the updates was "UEFI dbx - update to version 217". If I deselect that one, all the other updates run okay. But if I try to run that update, the system reboots.
Have I trashed something. I'm guessing fwupdmgr attempted to do some kind of UEFI firmware update - so something may be trashed in firmware that affects more than just the older OS where I ran fwupdmgr. Am I screwed - or is there a way to fix this? I suppose I could disable updates to UEFI dbx in Discover and hope that that gets around it... For now, I disabled the 'lvfs' firmware update service repository, and UEFI dbx no longer shows up as an available update. Is that kosher?
By the way, the package description for UEFI dbx says it has to do with updating secure boot signatures. I have secure boot disabled and Kubuntu installed without the shim (I think). I guess maybe that's why my system still works.