LTE data does not work on T-Mobile US with latest postmarketOS 21.06 SP3

[PacificSinewave]

I have a Pinephone Beta Edition (3 GB) running the latest postmarketOS 21.06 SP3 (kernel 5.13.12) Plasma and all updates installed (Discover does not show any updates when connected to WiFi and while Falkon works) and I have never been able to get LTE data working. I am on T-Mobile US network, have good reception, can see all the modem (IMEI) and SIM (IMSI, Subscriber Number etc) information and have received text messages and calls but mobile internet refuses to work (it is not just the browser either as apk is not able to connect either with WiFi disabled). I have verified the APN settings as well and they match what is listed on T-Mobile's website. I have tried turning Mobile Data on and off in the Plasma Control Center, rebooting, various combinations of those and changing the Authentication Method in APN settings. I am perplexed (as it seems that for those who cellular related issues it often is messaging and calls and VoLTE that do not work properly while LTE data does) and also a bit frustrated by this (one of the main reasons I decided to get a Pinephone right now is that it would be better for tethering than my iPhone, especially with the USB C dock that comes with the 3 GB version). Right now there is no check mark in the 'Active:" box below "Internet" on the Cellular Networks -> Access Point page of the Plasma System Settings app but even when there was, internet would not work, even though the AP type is listed specifically as "internet".

[beta-user]

@PacificSinewave
I'm on Mobian and mobile data never worked for me reliably, but I was able to get it to work sometimes. I think it only works over 3G, but I'm not entirely sure.

I tried setting Network Mode to 3G only in modem settings just now and I got a connection, so maybe you can try that.