Unable to connect to matches

Friend is trying to play multiplayer with me (PC - Steam) but every time we load into a game he gets booted to the title screen.
Tried: uninstalling; verifying game files; moving from SSD to HDD; port forwarding for steam; signing in and out of xbox live; Wifi and Lan.

We’re at our wits ends.

Has anyone had a similar issue and figured our how to fix it?

We’ve checked the forums and online the best we could but just have had no luck.

Any help is appreciated.

Thanks,

Edit: For anyone who has this issue: turns out my friends router settings had UPNP disabled and the setting buried stupidly deep (Vodafone Ireland).
Simple fix for what was a really stupid problem. Should have caught it sooner.