Not sure what you mean by MVNO, but its been a long issue for me trying to use the hotspot. I have a T-Mobile SIM in the r1 as well its nice to know you have more options.
A mobile virtual network operator(MVNO) is a wireless communications services provider that does not own the wireless network infrastructure over which it provides services to its customers.
T-mobile is one of the providers that has multiple MVNO’s on their network, and there have been multiple users reporting issues with T-Mobile.
2 months later and still T-Mobile SIM card does 1 question per hard reset. 
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Idk if it’s a fluke or not but recently like the last week or so i noticed my tello sim started working again. Like the only place i had it fail was a place in town where my cell phone usually loses service. So idk what changed but tello has been working again for me in my r1.