"Session Unavailable"

[(PSN)Mahd2_7 105]

Basically I've been getting thus notification alot more recently in I'd say the past 3 days where if I try to join a game it'd put me in the loading screen and then just before it should load in it says session unavailable and brings me back to my orbiter 

[(PSN)Reptiletc 18]

This has been happening to me on Ps4 for months now. It only happens to the first mission I try to join after firing the game up though.

But it is something I can replicate every time I start the game up.