Also POI must be away from city. That could be a reason you are getting calls like that.
I can tell you why this is occuring, to prevent players building stations ontop of each other, the game has an anti cheat system that spreads out the missions. You are trigering this system so to prevent you farming loads of credits, the game is spreading out the missions so you earn a resonable amount per hour just like players who have stations spread out.
Thank you very much, both of yours answer!