This problem has plagued the game since time immemorial on PS4.
Truth be told, I don’t think it’s the game’s fault. I don’t think I had to open up any ports on my connection’s router. You could try some basic testing, but you’ll need a PC for this. Stuff like ping, traceroute and telnet.
You may both need to raise a ticket with your respective ISPs, but they’ll want you to do the aforementioned testing first before they’ll proceed. Depending upon the ISP, they may assist and instruct you with the testing - not all techs are created equal…