cnMaestro unreachable (even by ICMP) from 450 SM

I have an issue with PMP450 SMs losing connectivity to cnMaestro and showing as offline. (I'm posting this on both forums as it is either an SM bug or a cnMaestro client bug)

The cnMaestro (self-hosted) IP address keeps appearing in the SM ARP table with an MAC of 00:00:00:00:00:00 and disappearing. This behaviour is visible during cnMaestro connection attempts and ICMP tests from both sides (cnMaestro and SM). cnMaestro is not in the same broadcast domain as the SM.

The SM is bridged, and all other SMs on the same BHS, as well as the BHS itself can reach cnMaestro.

This issue is usually resloved by a reboot of the SM, though todayI have a case where it was not resolved by an earlier reboot (cnMaestro shows it offline for >16 days). I believe this may be because post reboot the SM was not associated with the BHS for ~2 hours due to a color code mismatch.

The issue has occured on multiple firmwares, currently happening on, 16.1.1 and though has happened on 15.x firmwares previously.