EDIT: Very perplexing. I looked at your savegame. You’re properly zoned from the Security Checkpoint all the way to the Stand. I even changed a few of your other GA stands to Commercial, and the problem still existed. A definite bug.
Looks like you’re not the only person with this problem: Go to message 1174
https://forum.apoglabs.com/t/airport-ceo-alpha-35-released-the-terminal-update-experimental/15718/1227