Well I’ve certainly got no good guesses for the behavior that I and other people have seen, none that explains that other people with identical hardware running the same firmware with the same configuration seem to have no problems. iirc nothing too productive came up in ofono logs before when they’ve been posted either. @robthebold 's post indicated it might have something to do with dropping the network, which is definitely a common thing here, but that wouldn’t explain why I’m able to take the sim out and put it back in, reboot the phone, etc when I have good signal.
@flypig I’m not sure of the percentages, but would it be worth adding a caveat on the T-Mobile entry for the 10ii that these problems have occurred and that T-Mobile’s official position (at least from what their engineers told me,) is that a 10ii as a device isn’t accepted/supported for BYOD on the network?