Issue with RCS messaging while on T-mobile 5G WiFi

I have an iPhone 14 with the latest iOS which added the RCS messaging feature. At home I've been using Spectrum internet for years but last week I decided to try out the T-mobile 5G Home Internet. I got the gateway, set it up and connected my desktop, laptop and my phone to it. Everything was working fine and internet speed is great on all devices. But after just a little bit of messaging back and forth with my gf who has an Android phone, I noticed messages reverted back to SMS. I checked settings and everything is set to enable RCS. I then switched back to the Spectrum WiFi and messages automatically switched back RCS right away. But as soon as I switch back to the T-mobile WiFi, it goes back to SMS. If I restart the phone, then RCS works for a few minutes then it stops working again. I've searched all over the web about this and can't find any solution or even the reason why this is happening. Others have had similar issues, but does anyone know why this is happening? RCS seems to work everywhere else I go...works on cellular data and works on other WiFi networks that I've connected to at work or at my gf's house, as well as my Spectrum network. But it doesn't work on my T-mobile home WiFi. I don't get why, it makes no sense, but it's driving me crazy!