After having a two month long break, I cant find any matches, though I could before. I turned off/on firewall, even turned on Windows defender and security services again, but no results at all. I don’t have any Hamachi or similar to it software, I turn off 3rd party anti-virus before playing the game. But I stiil can’t play in multiplayer.
Is there anything to fix it?
everything else is working except KI?
Yes.
Go here, https://support.xbox.com/en-US/xbox-on-windows/social/troubleshoot-party-chat
and do the 2nd solution 
this fixed it for me 
Unfortunately, this did not work for me.
I’ve been in the same boat since the Gargos patch. I rarely find online matches any more and when I do it is Bronze or Gold players. I rarely play Killers.
Nat is Open. All other games work fine. It can take up 15 minutes to get a match.
Can confirm that none of this solutions from:
http://support.xbox.com/en-US/xbox-on-windows/social/troubleshoot-party-chat2
Did not help me in the slightest. Though I did not check the last option, because my router is from different manufacturer, and there should be no change to any of it option. I try with the router, if I would have any possibility to set it.
teredo issue does not help me on support.xbox. i tried anything to be honest i even search reddit but still same.
There was no properly written solution which was used to solve my problem, so I would write it here:
Go to Regedit
Go to the key:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters]
HKEY_LOCAL_MACHINE
\SYSTEM
\CurrentControlSet
\Services
\Tcpip6
\Parameters
And change the value of “DisabledComponents” to 0.
It works again now.
This is how you fix it fast https://www.youtube.com/watch?v=vpDPpF_EC_s
Saved my life !!! Thank you !