Not a question but an information post for someone in the future to dig up.
Opened new Tmobile One account and multiple lines. Transferred multiple numbers upon receiving sim cards (from Tmobile prepaid). One line could make and receive calls and texts, but did not connect to LTE data. Tested for device/phone issue by moving the sim to working phones, the line did not work in any of the phones.
SOLUTION: Call 611 and ask for technical support, explain situation and tell them it is a problem with the line and Tmobile's side. Insist it is NOT a device issue to save time. They will suspend the line, reset/restart the line so it has all the correct settings for the Tmobile plan, restart your phone. This process will clear all your voicemail but I recently ported so nothing major. Total talk time: 17 minutes after getting tech support to realize it was Tmobile's problem.
Underlying problem: Purportedly had to do with some settings on Tmobile's end during the transfer process that did not enable that particular line to work with the Tmobile One unlimited data plan and was also causing my phones to adopt the wrong settings. After line reset and phone restart, all good.
Don't bother: Chatting or going in store or getting a new sim card, despite what chat or tech support tells you. Total wasted time: Over 2 hours...