iPhone 7 T-Mobile Wi-Fi Calling & SMS over Wi-Fi

I recently upgraded to an iPhone 7 from a 5s running 10.2.1. I've been having a few issues related to Wi-Fi calling and sending SMS/MMS messages while connected to Wi-Fi.

Wi-Fi calling and SMS over Wi-Fi always worked seamlessly on my old phone, but I've been having quite a bit of trouble with it on my new one. When I restart my phone and connect to Wi-Fi, I see the "T-Mobile Wi-Fi" indicator at the top of the screen. However, as soon as I try to make a call or send a message, it doesn't work and the "T-Mobile Wi-Fi" indicator switches back to "T-Mobile". Once it stops trying to make the call over Wi-Fi, it goes through fine.

I've also noticed that I've been getting really delayed SMS messages (especially group messages or MMS messages) - this happens a lot when I'm at home and connected to Wi-Fi - once I leave the house and lose my Wi-Fi connection, all my messages will come in at once. I also have a lot of problems when sending MMS or SMS messages when connected to Wi-Fi. It's almost like the phone thinks it's still operating over Wi-Fi when it isn't.

I've tried a network reset and checked to make sure Wi-Fi calling is enabled, that my carrier settings are updated (T-Mobile 27.3), and that my emergency address is updated - nothing seems to solve the problem. For the time being, I've turned off Wi-Fi calling and it seems to fix the problem, but it's a nice feature to have if I can.