Hi jmjones,
Thanks for your test details and reports.
Are you using the 3.6.2 build 1398 on the AP One AC mini hw1? We found that 3.6.2b01 mesh connection have compatibility issue with 3.7.3 and 3.8.1 AP One firmware and fixed the issue in latest RC firmware.
If you are already using the RC firmware on both Mini and AX, could you please help to open a support ticket with diagnostic reports from both APs? We can check the root cause from them.
Thanks,
Lewis