I have a friend on PS4 who I've been talking to for years. About 4 days ago I started having serious NAT issues with him. Whenever he joins a party I'm in I lose connection a few seconds in. When I join back I can sit in the party for a couple of seconds. However, I can't hear anyone due to NAT issues. These are people I would otherwise be able to talk to if this person wasn't in the party. After, sitting there for a couple of seconds and not being able to hear anybody it boots me from the party. Not only will I get disconnected from the party when he joins: but I also lose connection to whatever game I'm playing. However, it doesn't take me 100% offline.
My friend and I both have Type 2 NAT and we haven't messed with our internet. We don't have lag issues or connection drops. So this just came out of the blue.
I have tried a multitude of fixes to no avail. I have done simple things such as restart my console, and router/modem; and I've done more advanced things such as forwarding ports, and putting the PS IP in to the DMZ (Which I deactivated after because apparently it's a security risk). Furthermore, I've tried contacting my ISP and all they suggested were things I've already attempted. I even had a women call my PS4 a Gameboy and give me a link to a Nintendo website. Hilarious... But not very helpful. The only thing that was suggested to me that I haven't tried is hooking my PS4 directly to the modem/router: however, this isn't an option for me.
It's very important that I find a fix for this. He's part of my main friend group: so when he's online I can't talk to anyone and just end up playing single player games. Sure we could talk on Discord or something but that's a temporary solution. I really need help with this issue before I end up having to swap out my modem. 