I use SSH keys stored on a Yubikey. Today I got the following message when adding my keys to the ssh-agent, as usual:
$ ssh-add -K
Enter PIN for authenticator:
Provider "internal" returned failure -4
Unable to load resident keys: device not found
There have been no updates to SSH recently. Restarting does not help.
System:
How do I debug this?
I don't know what went wrong exactly or how to debug it, but this helped me fix it:
Install the Yubico Authenticator app from the Mac App store. Plug in the Yubikey, open the "WebAuthn" section, enter the PIN, and suddenly you can add the SSH keys to your agent again.