Hey, are there any other logs that I can grab? Is there a way to override the defaults, which will allow me to use the right key to sign?

I'm not really sure which version it worked with earlier. This yubikey setup is quite old now, and I've not signed keys recently. I think the last I signed were at least 2 yrs back, hence the very vague allusion to the setup working previously. Apologies, no definite answer there.

Just noting that the logs were captured by enabling debug logs for the agent:

eval $(gpg-agent --daemon --debug-all --log-file /var/tmp/gpgagent.log)