I see the same issue, it seems to be impacting everything with libfido, ( ed25519-sk and ecdsa-sk SSH keys as well ) Reverting that commit also fixes the issue for me.
I don't see anything obvious in dmesg, running ssh-agent with FIDO_DEBUG=1 yields a small bit more information to go on: debug1: start_helper: starting /usr/libexec/ssh-sk-helper debug1: process_sign: ready to sign with key ED25519-SK, provider internal: msg len 186, compat 0x0 debug1: sshsk_sign: provider "internal", key ED25519-SK, flags 0x21 fido_hid_manifest: /dev/fido/0: vendor = "OpenBSD", product = "fido(4)" debug1: sk_probe: 1 device(s) detected debug1: sk_probe: selecting sk by cred fido_hid_open: inlen = 64 outlen = 64 terrible_ping_kludge: send ping 0 fido_hid_write: write: Message too long fido_dev_open_tx: dev->io.open debug1: sk_open: fido_dev_open /dev/fido/0 failed: FIDO_ERR_INTERNAL
