I'm coming towards you as since i've changed my modem / ISP, I can't play with someone else online on NBA2K2 anymore. (before that, I could only accept invitations anywho it was)
We have done multiple tests (we were 4) and we don't understand why there are no problems with some players but with the other ones, the invitations on NBA2K2 are impossible (I have videos that i can show you)
I tried putting DMZ on my Raspberry 3B+ (with Dreampi 1.7 DLE), NAT/PAT rules as well as disabling the firewall of the modem, trying in wifi with the same settings.
I've also tried with a different USB modem and an other Dreamcast but it doesn't fix the issue.
So I don't know what causes this to happen.