North Underrail doesn't appear on Metro's selection options...

[HulkOSaurus]

...after you defeat Tchort and SGS are hostile towards you.

Basically SGS went hostile towards my character, and I actually don't know why exactly, but it's most probably because Gorsky went hostile towards him in Core City at the Black Crawler's base. While I was trying to exit the area and fight the mutants, Gorsky and the Zone Rats went hostile on me.

Not a biggie as is, but it seems North Underrail doesn't appear as a selectable option even after Six tells us about it.

[PhrygianDominant]

You're right, it was because of Gorsky. Fixed that for the next update. What happens in Core City is going to stay in Core City from now on.

Also unlocked the option to travel to North Underrail as soon as Six tells you about Tanner.

[HulkOSaurus]

Sweet, thanks!