Hi limbot,
The mesh pairing is implemented by WPS, I checked your log. It says you don’t push the slave’s mesh/WPS button to trigger WPS communication, like
PBC Status: Timed-out
Last WPS result: None
If pairing fail, push both master and slave’s mesh button for 5 second.
You can use
hostapd_cli -i ath11 -p /var/run/hostapd-wifi1 wps_get_status
to confirm again.