I was building my airport when people stopped departing from my airport. Found out the metro passengers run up the stairs and immediately turn around and go home. The flights are still shown fullfilled and filled up correct. My shop doesnt make any money anymore. Zones are all correct. In the same game passengers had the same problem at certain stands and got locked. This happened especially with double row benches. Had this problem multiple times before. Found out that when I used the red zone again (dragging a redzone area in an already excisting red zoned area.) people moved normal again and could board again. I hope this information is usefull to you.
Im new to this forum. I want to post more stuff when i find bugs. If there is an area (which I havent found yet) this post belongs let me know please.