Mi 10 Ultra disconnectecting from cellular network

[seltsikp22]

I have a MI 10 ultra with the latest weekly rom. I'm based in the USA and have tried to connect to several mobile networks and keep having the same problem. The SIM activates and I can use 5G data, send SMS and place a call. When I try to place another call the network drops out - no signal - and it becomes impossible to restore the service. Resetting APNs doesn't seem to help. I'm on my 3rd mobile network now and the same just happened. Anyone have an idea what might be going on?