I have a x20-4G hooked up to a ISP provided cable modem through the first ethernet port on the router, and a SIM-card set up to provide 3G/4G failover. I also have a switch connected to the second ethernet port on the router, with various devices connected such as a pi-hole providing DNS with adblocking.

If I simulate a failover scenario by disconnecting the ISP modem from the x20-4G, the router correctly switches over to 4G. But the connection to the switch, which has not been physically disconnected from the router, goes down. Only the wireless devices remain connected. This creates several problems, but the main one is that I loose the pi-hole DNS, and consequently all wireless devices loose internet even though the router has successfully failed over to 4G.

As soon as I reconnect the ISP modem and the router switches back to wired internet, the wired clients also reconnect and all is well.

Is this intended behavior, disconnecting all wired clients when 3G/4G failover is active?