(Edited: this message originally had two separate issues, but one of them was my own misconfiguration, and has been edited down to one.)
I'm using RUTX09 with a single 4G SIM in bridged mode. I can no longer connect to RUTX09 if I set a static IP address on a computer. My LAN IP address space is 192.168.1.1, so before activating bridged mode, I set RUTX09 to use 192.168.2.1 instead, which worked. After activating the bridge, there's a strange issue: if I set a laptop (a MacBook Pro in this case) to ANY 192.168.2.x address manually, I get a complaint about that address already being in use, no matter what .x is. Pinging 192.168.2.1 doesn't work either. .2.1 is the only active address in the .2.x space.
The RUTX09 is running the latest-as-of-this-writing firmware (RUTX_R_00.02.01.1 dated 2020.01.15).