HiLink Huawei can't get cell signal in OpenWRT Pi, works on Windows Pc

This is confusing me. I have a Pi 4 running the main applications for my car (Mercedes Me on Home Assistant, J.River Media Center and a few other things). OpenWRT is running on a separate Pi3B. That has load balancing and connects to the wifi when I'm at home and should use the Huawei E3372 in HiLink mode when the home network isn't available (if pinging doesen't answer). But I can't get it to work.

I had it working with another, identical modem that I had to send back (unrelated issues with the web shop, not the modem) but this just won't work. have no problem accessing the Hi Link network address (, but I see there that it says "no service". When I connect it to a Windows PC it gets service at once.