I'm definitely sorry to hear you're having this issue, and I want to make sure we get you all squared away. Since a SIM card change appears to have led to this, I'd recommend contacting our Beta team at 1-844-889-5651 from 3:00 a.m. to 10:00 p.m. PST.
At the same time, you can check your set up on T-Mobile.com as well to make sure everything looks correct. On T-Mobile.com, check your multi-line settings (steps here: Virtual line and duplicate line setup for DIGITS). Please make sure your line is listed a as line you can use, not just a line you can manage. Also, please make sure the T-Mobile ID you are using is tied to both the primary line and the duplicate line. Finally, please make sure you are signing in with the T-Mobile ID, not a mobile #.
Hope that helps!
All lines have been working well. For the most part it's been pretty smooth. Every once in a while a a line would temporary disable. or say temporarily unable to connect. No problems for at least 48hrs. things are good. Thanks for checking in.