MMS won't send over Wi-Fi with Verizon phone

I have a Verizon Galaxy S9 plus and my mom has the S8 Plus. Both phones are Wi-Fi calling capable which also includes WiFi messaging.

I have no problem sending MMS when I'm on a public Wi-Fi network but when I'm at home it just sits there forever and finally fails. I've tried turning the security off on my home network and it still will not work. Text messages (sms) work fine even when I turn it on airplane mode with mobile data off. However MMS just won't send. 

I've tried all kinds of things I've read on the internet such as opening up ports 500 and 4500 under NAT gaming to no avail.

Right now my solution is to use the Verizon Wi-Fi messages app which includes native WiFi support. I'd like to be able to use the app of my choice.