Hi there, PLEASE SHARE THIS WITH ANYONE PERHAPS they might make it work themselves!
1. YES, either ISP blocking via their IDS (instrusion detection system) if seeing suspicious activities OR
2. AS THE BELOW, your firewall router might be a root cause. NO, it is not required port triggering enabling OR port forwarding, the Server-Client Application network service ingress-egress handles the dynamic inbound/outbound protocols/port and the firewall handles as the standard communication. It is the IP blocking features in the firewall causes the network service disabling so server-client application network service communication is no longer working.. please see below as I just fixed my case.
I think I found the root cause of this problem. I started having the issue that I could not play any other game mode EXCEPT Core TDM and Zombies. It started on Friday last week. So I opened the ticket support with Activision, they preferred to static IP and open number of TCP/UDP ports.
It turned out it was the network service filter I enabled on my AC68U (Asus RT-AC68U) recently to block the external IP address blocks from Amsterdam/Europe were trying to exploit my router as I saw in the logs. I removed the IP blocks but forgot to turn off the Network service filter. When I disabled the network service filter feature (by default it is disabled), I was immediately able to join to any game mode like 15-90s...no more long wait in Core TDM as well.
Network services is the term when Server-Client Application communication ingress-egress on a set of protocols/ports such TCP/UDP. By enabling Network service to filter "network services", that means it now starts blocking,rejecting Server-Client application dynamic ingress-egress protocol/ports communication than the common tcp such 80, 443, 21..etc.
You might take a look into your Wifi Firewall router and into the network filter or IP blocking configuration and make sure they are disabled. It then should work!
Additionally, Those IP addresses I found was trying to connect through my firewall were from Ireland's DemonWare.net, it is part of Blizzard/Activision. First I enabled Network service filter and blocked 16bit of their IP that actually caused issue but I also removed those network id/16bit out but I didn't disable the network service filter so basically two things combined.
Just make sure you do not enable individual IP blocking service, configuration in your firewall router then it should resolve your issue!
I'm not sure how to check if it's blocked or what - I mean I can see on the Info area in the game what my IP and location and everything is, but everything seems fine from what I can tell.
I'm also using a GTX 1080 with Ryzen 1800x and 32gb ram, so I'm good on that front.
I just went to support and updated my ticket, so hopefully it gets ironed out soon. Honestly, part of me is relieved that it didn't happen until after the quad feed even wass over But another part of me is like F this game. :/
It is in your router's options and/or configuration...check some places like firewall or advanced...etc.
What wifi router brand do you have? I can look it up the configuration and tell you where you should check and make sure it is disabled (by default the network service filter or manual ip blocking is disabled by itself)