Not to add to the mystery, but

Was already on 2.5.10, downloaded 2.5.20, launched and immediately did a force update (UF), worked on the AX88u and both AX86u's and do get the expected response

Worked/Working for me...
But when launching it the first time via AMTM/J3, something scrolled by so quickly I couldn't capture it, even after 3 tries
Spoke to soon, somehow it messed with the ntpMerlin config, Time stopped synching and in scMerlin NTPD started when selecting 8 in scMerlin
Had to set it to NTP, then Chrony and save the config both times in ntpMerlin, then the 8 option in scMerlin and chronyd started up and Time began synching again.
May 12 13:51:37 Router ntpMerlin: Sleeping for 5s to allow firewall/nat startup to be completed...
May 12 19:43:58 Router chronyd[7279]: Source 68.183.107.237 replaced with 83.147.242.172 (1.us.pool.ntp.org)
May 13 09:03:38 Router ntpd: Started ntpd
May 14 19:55:03 Router chronyd[7279]: chronyd exiting
May 14 20:00:43 Router [22317]: initial drift restored to 9.465000
May 14 20:00:43 Router [22317]: Listen normally on 0 lo 127.0.0.1:123
May 14 20:00:43 Router [22317]: Listen normally on 1 lo:0 127.0.1.1:123
May 14 20:00:43 Router [22317]: Listen normally on 2 br0 192.168.1.1:123
May 14 20:00:43 Router [22317]: Listen normally on 3 lo [::1]:123
May 14 20:00:43 Router [22317]: Listen normally on 4 br0 [2600:1700:3d51:1c8f::1]:123
May 14 20:00:43 Router [22317]: Listen normally on 5 br0 [fe80::264b:feff:fe09:c9a0%46]:123
May 14 20:00:43 Router [22317]: Listening on routing socket on fd #22 for interface updates
May 14 20:00:43 Router [22317]: kernel reports TIME_ERROR: 0x41: Clock Unsynchronized
May 14 20:00:43 Router [22317]: kernel reports TIME_ERROR: 0x41: Clock Unsynchronized
NTP was/is disabled on the Router, it was using this setup when restarting Time Sync (8) via scMerlin
Fixed now!