Static vs DHCP setups from ModemManager in OpenWrt

[Peter Naulls]

Hello all.

I'm using ModemManger 1.16.6 on OpenWrt along with its scripts (and slight 
modifications so it doesn't just give up in the end).

After a lot of testing and loss of connectivity, it seems that although
our provider is offering DHCP, the connection via ModemManager is configured
statically. This leads to loss of connection after several hours unless
intervention is taken such as manual DHCP or re-configuring the interface.

We can see here:

# mmcli --modem 0 --bearer=1 --output-keyvalue | grep ipv4
bearer.properties.ip-type       : ipv4v6
bearer.ipv4-config.method       : static
bearer.ipv4-config.address      : 10.246.110.163
bearer.ipv4-config.prefix       : 29
bearer.ipv4-config.gateway      : 10.246.110.164
bearer.ipv4-config.dns.length   : 1
bearer.ipv4-config.dns.value[1] : 107.112.229.135
bearer.ipv4-config.mtu          : 1430

So the question is, is this a ModemManager bug? Or is it misreporting
from the carrier, or something else?  What can I do to debug this?

Thanks!