I've searched high and low to see if I could hunt down more info but unfortunately found nothing. You're off to a great start by using our BYOD data and APN settings, but beyond that the only info you'll likely find will be from other users.
That's probably a good setting but you may find a few places where T-Mobile's only usable signal will be 2G GSM. I'm a tad concerned that you may be blocking access to 2G if you need it. Have you tried doing a network settings reset?
I have the same issue with my unlocked Verizon Samsung galaxy note 5. It worked for 2 months, now nothing.. Also happened with my AT&T LG.. Getting annoying! I can call out but incoming calls go straight to voicemail. My phone will send texts when it feels like it and receives them late, if at all.