Loss of IP connectivity

This old thread doesn't seem to reach a conclusion and I am experiencing similar problems with a Netgear Nighthawk M1 running firmware version NTG9X50C_12.06.39.00

 

In my case the M1 is getting it's IP address from the 4G mobile network operator.

Because the DHCP request from the M1 is going out over the LTE interface I have no way of using wireshark to see what is actually happening.  As the M1's admin interface does not appear to allow me to see the detail of the lease assigned to it I am unable to identify DHCP lease renewal as being the root cause.  As the M1 does not allow me to do the equivalent of IP config /release /renew my only recourse is to either wait for it to mysteriously start working again, or reboot the M1.

 

Around midnight on most nights, when the M1 has a Vodafone UK SIM in it, I experience loss of IP connectivity to the wider internet. At no point is there any evidence that the 4G signal has dropped.  If I wait long enough, then data packets start reaching their destination again.  If I reboot the M1, then data packets start reaching their destination as soon as the reboot completes.

 

Oddly, when the M1 has an EE UK SIM in it I do not experience the same regular loss of connectivity.  This makes me wonder whether Vodafone has implemented a much shorter lease time (24 hours) than EE, or whether the interpretation and implementation of DHCP is subtly different between the carriers (assuming DHCP is the root cause).

 

Any ideas - or ideally a fix - would be great.