Hello, dear community!
I am having this problem ever since spring 2018, and it was really frustrating, especially, because nobody was able to help so far. I was home in Austria for some days, and the game went fine, then back in germany for a month, and then back to austria again, and i just couldn't connect to like 90% of all people anymore. I was able to log in, talk to people, and connect to some people, so i was able to play some 1v1 games. If i have done something to cause all that, then I sadly don't remember... I just came back and was unable to connect to most of the players.
I tried port forwarding with your instructions, which didn't work, except for one time when it got me into games again, but these games crashed after the first frame.
The port in the options is 16000.
I reinstalled the game as well, didn't work.
PLATFORM: I play on Windows 10.
VERSION: I play with the normal KW that I bought when it came out.
I got the log as requested in your thread, and the results from the bat-file (after DMZ and port forwarding were deactivated)
Using server nntest.cnc-online.net:30000
Bound to local port 52909
Bound to local alternate port 52910
Resolving hostname 'nntest.cnc-online.net'...
Resolved server host to be '188.8.131.52'
Sending client INIT from port 52909 to nntest.cnc-online.net:30000
Received server INIT 
Our public address is 184.108.40.206:2373
Sending client INIT2  from port 52910 to nntest.cnc-online.net:30000
Received server INIT2 
Our alternate public address is 220.127.116.11:43292
Sending cient START  from port 52910 to nntest.cnc-online.net:30000
Received server START 
Server extra port is 40000
Sending client PING  from port 52909 to nntest.cnc-online.net:40000
Received server PING(2) 
Received server PING(3) 
Received server PING(4) 
Received 3 pings from nntest.cnc-online.net:40000.
NAT negotiation works with your router and connection.
==> You do not have to use port forwarding.
Drücken Sie eine beliebige Taste . . .
I already thank you for your time, and i'll be happy to help you help me!