I have one key that has "missing keys". It shows a resource ID, but that's it. I would happily delete it, but I do not know how to delete using ID only. No other actions are offered.
Annoyingly, now there is a wide bar on top of Joplin desktop: "One or more master keys need a password. Set the password". How do I remove that? I tried to clean install and re-sync, - the same story.
Missing keys:
The keys with these IDs are used to encrypt some of your items, however the application does not currently have access to them. It is likely they will eventually be downloaded via synchronisation.
By now I disabled the encryption and downloaded all notes again. Now I have two keys that I cannot access. Those were generated when I tried to use Joplin cloud. Originally, there was only one key.
I had the same problem. I only had a few notes, so losing everything was not a problem. I had to uninstall Joplin from all devices and delete all file and folders in the Joplin folder in DropBox. It's in the apps folder if you have problems finding it. Problem fixed. Only setup a master key on one device. Each additional device will ask for the master key when it syncs. Just be sure and do not configure encryption on additional devices, they will ask for the password the first time they sync. Hope this helps.
Thanks for the information. It turns out that a new "missing key" is generated every time I turn the encryption on. I ended up turning off the encryption on all devices, syncing, and turning it back on. The erroneous keys are still here (disabled), but the banner is gone. Still, I wish I could just remove those keys because they point to the assets in sync source (Joplin cloud in this case) that is no longer available for syncing.