FreePBX12 maxexpiry Setting vs SIP Show Registry

Hi everybody,
I have recently been building a FreePBX 12 system, and am using an Engin SIP trunk. It looks like everything is working pretty well, but that my registration to Engin is timing out sporadically. It seems that inbound calls just stop being sent to my network on an irregular basis. When this happens, the connection never seems to return. I have set my Registration Settings as:

minexpiry: 60
maxexpiry: 900
defaultexpiry: 180

I’ve been using a Sipura SPA2000 box to connect to Engin for years and checked the expiry that it’s been using successfully. It’s using 165 seconds.

The interesting part is that when I enter the command “sip show registry” via the CLI, the result I get looks fine except for Refresh, which is 3585. It doesn’t seem to matter much what settings I use as the Refresh reported in the CLI is always 3585. I’m pretty sure this is the reason why my registration is dying.

Looking inside the SIP conf files I can see that the settings reflect what I have entered via the GUI. I just thought that I would ask if anyone here has noticed this problem before, or better still, might have a solution or recommendation for how to get the system to use the registration times that I’ve set…

Thanks, and best regards