Not recieving SMS without an internet connection

I have an iPhone 12, as well as a cellular provider with unlimited SMS talk/text. I have both iMessages and SMS messages turned on in my device settings, with Send & Receive set to my phone number.

I'm in a group chat that has someone with a android device, so from my understanding everything in that group chat is SMS. Everything sent is a green message bubble, so as far as I know imessage and internet connection shouldn't factor in at all.

The issue is, I only receive texts from that group chat when I do have an internet connection, and specifically only when connected to data, wifi is inconsistent. If I have data off, I stop receiving SMS messages. Why is that? How do I fix it? (If possible I'd like a fix without having to disable iMessage entirely, but if it's the only way oh well.)

Additional information that might be relevant: When I have no internet, I can still send SMS messages and they send normally, I just don't receive anything.

I found a similar issue which had a response claiming that iphones default to imessage when wifi is off, but that made no sense to me.