"signing failed: agent refused operation" error occurs

When connecting to sshd on CentOS6 from MacOS using ssh-agent with 1password, the connection fails with the error "sign_and_send_pubkey: signing failed: agent refused operation".

I have summarized the code and how to reproduce it in Docker at https://github.com/masahide/1pass-agent-refused

1Password Version: 80700031, on NIGHTLY channel
Extension Version: Not Provided
OS Version: MacOS11.6.1