No one at T-Mobile has been able to help me so far, either in store, on the phone, or elsewhere. I am describing my situation in great detail and keywords, so as to help others facing similar difficulty, so excuse the length. I'm trying to help you help me, because my job depends on my ability to securely transmit encrypted data intended solely for its legal recipient. Besides, I know I'm not the only one who is having VPN trouble.
I've noticed T-Mobile is quick to decline assistance in other services or apps; however, through my own tests, I have been able to determine the problem only occurs when I am using T-Mobile's mobile network and must therefore be addressed through T-Mobile. And because the people on the phone and web chat can only "apologize for that one," I am forced to come here for answers from people who actually understand the nuance of this issue.
A brief description of my problem:
I connect to my VPN, use it for a few minutes without problems, and then it stops working. The connection shows all systems are normal, everything is green and connected (and with full bars, no less!) but my connections time out and fail to load. Emails do not send until I disable the VPN service, and then all my notifications flood in at the instant I disable it.
Tests I have run:
1) This did not happen when I was on AT&T, prior to switching to T-Mobile using the same phone
2) This only happens when attempting to use T-Mobile's LTE/4G network
3) This connection problem does not happen on wi-fi. The VPN behaves normally until I disconnect from wi-fi and the phone kicks back over to my mobile network
4) My VPN works in all other situations and devices, and never stutters or fails (I am also using one of the largest, most reputable leading VPN carriers in the world)
5) I factory reset my phone, to no avail. The problem remains exactly the same
6) I have set up the VPN manually, using the three major protocols, all with the same outcome
7) I turned on airplane mode for 10 seconds, and turned it off again. While this gets VPN working immediately, it does not solve the problem of VPN failure after two minutes.
8) I restarted the device
9) I turned data roaming off, and back on again as that did not help either
Afterthoughts, possible explanations and conclusions:
An agent who attempted to help me suggested maybe T-Mobile doesn't want people using VPNs on their networks, either because it hinders their ability to track and sell my data to third parties, or because T-Mobile doesn't want people concealing their "hotspot" traffic, thereby circumventing throttling rules. That just sounds like a conspiracy to me, but at this juncture, we could both be wrong. He has a point, though, as money is all the motivation any company needs to implement hidden anti-consumer policies. Again, I'm not saying that person is right or wrong, but he and I are both relatively uneducated when it comes to the inner workings of cellphone networks, so of course we are prone to believing conspiracy theories in that area! I do hope he's wrong and there is a fix for this technical problem.
I've seen complaints of carrier update 28.3 breaking VPN traffic, because of IPV4-only apps not yet ready for an entirely IPV6 world. If there is any veracity to this claim - that is, if my problem is related to my VPN using IPV4 and the LTE network switching exclusively to IPV6 - then why would my VPN still work for two to four minutes, before dying? I saw similar complaints regarding the iOS 10 update, but that does not perfectly match my problem. It looks the same, but it's fundamentally different.
Just a side note and follow-up question:
Interestingly enough, my lock screen notifications appear, and contain the contents of the message, but when I swipe the notification to open the program, the content does not load in. It will not load until I disable the VPN, or switch the phone into airplane mode, and back off again, forcing the VPN to reconnect on demand (Connect On demand). Could it be that this content loads in on the regular LTE network, but my actual interfacing with the apps fails through VPN? If that were the case, then it breaks my understanding of what "Connect on Demand" means, or a failure on Apple's part to respect the importance of Connect on Demand. In any case, I would love a solution to this problem!