You are exiting to main menu, when you proceed to score screen, so yeah. You could also try reloading one autosave before the winning one and complete the game again.

Sublustris wrote:

You are exiting to main menu, when you proceed to score screen, so yeah. You could also try reloading one autosave before the winning one and complete the game again.

I did that countless times to no avail. The achievement doesn't pop up.

Wasn't there an option out in (Endless) Space (2) to play on, instead of going to score screen? I can be wrong about, but if it's possible choose this one and end turn, for to get the achievement.