100% reproducible.
I wonder with the zoom in/out is an attempt by devs to now overload the map by drawing 100s of icons etc…so perhaps some limit is in place.
not a very good approach, but I could see how there might be issues if you zoom right out, when you have unlocked every mission type 
ofc, the obvious solution would have been filter by mission type.
… which you have to think, must have been original planned by didn’t get implemented in time. ! its kinda crazy its not there on day 1.
yeah, I noticed this today too…at a smaller airport.
means there could well be many more missions that we just never see.
(my guess is, they are just drawing the icons on top of each other… so its random which icon you get to see)