LM1200 repeatedly dropping link

I have just purchased and setup an LM1200 in combination with my Unifi network at home (in Australia). It seems to be working well. Have setup the LM1200 first connected to a laptop, making sure it connects to a mobile network, setup in bridge mode, etc, etc.

Then I've connected the LM1200 from its LAN port (not the WAN port) to port 10 on my UDM-Pro. Configured the Internet settings as having a dual WAN, with port 10 as the fall-back. Then configured the port 10 with a WAN profile. The last step is only possible after the Internet settings have been configured with the dual WAN config.

Everything seems to be working well. When the primary WAN is active (connected to my gigabit HFC cable internet connection), the LM1200 is not visible, i.e. 192.168.5.1 is not reachable. When I disconnect the primary WAN internet connection, fall-back to the LM1200 and mobile network is done within the minute (possibly quicker). Once that is the active internet WAN, the LM1200 management interface becomes accessible through the 192.168.5.1, and you can see the health of the mobile connection, etc.

When the fixed primary WAN becomes active again, the LM1200 becomes inaccessible again after a minute or so. Everything seems to be working fairly smoothly. I've also installed an omnichannel antenna and connected it with the two wires to the LM1200 for increased mobile reach and therefore performance. All together it seems to work well as a relatively cheap internet backup solution.