Friendly Co-Op Trouble

[Noblefaun]

So i've been playing Warframe for quite some time now, but one of my friends just started playing again. 

The problem though is neither him or i can join each others session, we can easily join other of our friends/invite other friends to games, but we cannot invite each other.

 

Anybody knows what might be wrong here?

 

Thank you in advance

[Angius]

Go to the options -> diagnose connection, or something like that. It is possible, that one of you has Strict NAT.

[Noblefaun]

Says everything is working, so there is no Strict NAT :/

[AdunSaveMe]

i know it's a stupid thing to ask, but JUST IN CASE...

 

Are you sure you're on the same region?

[UnknownBlademaster]

Both of you verify your game caches and restart your routers, then restart your PC's and try again.