When I originally jumped through hoops to get this setup working (after spending ages with VM support, including paid support, without success) I ended up connecting a computer directly to the VM modem via ethernet patch cable, allowing the connection to become established, then cloning the laptop MAC address into the router.
Every now and then the modem/router lose the connection to the VM network. To fix that I have to plugin a computer via patch cable to VM modem again to establish the connection.
I can then unplug the computer and the network connectivity will resume service as normal, even while leaving the MAC address the same in the router.
I'm assuming this is *something* to do with VM security stuff forcing something to reconnect that I guess is working in a way that is incompatible with the router (or the current router settings).
So the questions is, can anyone here advise with any certainty what might be causing these VM<->router connection loses and what setting should I be looking for in the router to prevent it happening in future?
Might be worth looking at the 'DHCP query frequency' setting on your setup and see if that does anything to help you.
Assuming I have looked at the right model, your router also seems to show a recent firmware update of 13/7/20 though does not seem to describe anything specific to your problem in the description for that. (It is unclear if the 'Continuous' setting described above only becomes available with the latest firmware. You'd need to read the above topic and links to decide).