"Join session failed. Error Initializing network layer"

[AND]

Finally fixed this issue after resetting my router, changing my IP, uninstalling all workshop items, clearing cache a million ♥♥♥♥♥♥♥ times and uninstalling the game twice.

Managed to fix the issue by simply opening the game file and launching the 'Squad_launcher' application through running as administrator. The issue must be something to do with the anti-cheat conflicting with whatever firewall settings you have on.

Hope this helps.