I have been having issues with our ZD management ip's MAC switching to the smart redundant ZD and locking us out of the web interface. To resolve this we just clear arp on the router for our management IP and this clears the issue. However this locks out client authentication for a short time before it can be realized.
Flexmaster logs shows TR-069 client registration at the exact time our management IP switches over. Can this protocol be turned off or does Flexmaster use it to communicate with the ZD's?
Your versioning may be the root of the problem - you have to keep FM in sync with ZD on upgrades. FM 9.5 doesn't know anything about the future (ZD 9.6..) - it only knows about ZD 9.5 (and below) and sometimes the interfaces change.
Did this problem start after you upgraded to ZD 9.6?
I can definitely try and update to FM 9.6 and see if this works. This has been happening for quite awhile. I can't remember if this issue occurred before we broke sync at 18.104.22.168.29, need to check our logs to be sure. I will try and sync the software and hopefully this fixes it.