I had swapped it to that and encounter the same issues

Name T-Mobile
APN epc.tmobile.com or fast.t-mobile.com
Proxy blank
Port blank
Username blank
Password blank
Server blank
MMSC http://mms.msg.eng.t-mobile.com/mms/wapenc
MMS Proxy blank
MMS Port 80
MMS Protocol WAP 2.0
MMC 310
MNC 260
Authentication type Not set
APN Type default,supl,mms
APN Protocol IPv4/IPv6
APN Roaming Protocol IPv4
Bearer Unspecified

sheesh54 are you using Google for Internet connectivity check/Attestation/PSDS Server? I'm not saying that will work but letting you know my settings. Make sure to restart after changing all that to be on the safe side. I'm no pro just letting you know how I am set up since mine works

sheesh54 Also, I'm using LTE only and this is my carrier settings (tmobile_us-40000000138.54)

I am not using Google for connectivity checks, also I had my device on LTE, but I changed to 5g as preferred and noticed no difference.
Not too sure, I can understand if it just wasnt working, but I dont see why itd work sometimes then not others

    sheesh54 I am using Google for all three of the above services. That may have no bearing on your results though.

    sheesh54 The only thing left I can think of is the VPN you're using. I'm using Nord. Sorry the above didn't fix your problem. Hopefully something will come along upstream and it'll be resolved soon

    The VPN is simply Wireguard, going to my home firewall. Unless it's an issue with the Wireguard app. But I doubt it seeing i works flawless on WiFi.
    Thanks for trying, maybe someone else has an idea.

    Curiously, where is this issue being tracked upstream? Just curious about it's progress.

      sheesh54 But remember no one has had problems running their VPN over WIFI. This is a carrier issue so it is possible that it could be how the VPN is communicating with the carriers network.

        Yes I am aware of that, maybe someone else can confirm if they are having Wireguard issues

          T-Mobile custom APN settings didn't help me and neither did the latest update. I use NordVPN WireGuard, but switching to OpenVPN doesn't help either.

          T-Mobile doesn't work via IPv4 at all in my area. If I use custom APN settings and select IPv4 or IPv4/IPv6, then I don't get any data conneciton regardless of VPN Lockdown usage. Exclusive IPv6 is the only functional APN setting for me that allows for data to work...

          I wish I knew more about the issue. There is a commit for it that describes eBPF changes, but that's too advanced for me. It has something to do with how VPN Lockdown setting treats inbound traffic on IPv6 networks.

          At least in my case, I get a good stable connection once I enable Airplane mode, disable VPN Lockdown, disable Airplane mode, connect to VPN, and re-enable VPN lockdown.

          I'm curious to know whether Google is aware of this issue and is actually planning to fix it? Has Google even confirmed awareness of this problem?

          I'd like to alert T-Mobile, Google, and VPN providers about this issue, but have no idea how to get to the right level of tech support and what information to provide. It has to be something specific network engineers can work with.

          Has the latest (October 2022) update fixed this issue for anyone? It didn't do so for me and Google didn't mention anything about it in its release notes. I doubt Google is ever going to fix this problem.

          This issue is big enough for almost all my clients to want to either downgrade to Android 12 or move to a different carrier that doesn't use IPv6 or at least doesn't use IPv6 exclusively.

            8 days later