@FlyingRaccoon @EPellissier we have the same issue and reported here:
Unable to spawn at some locations (with or without an airport addon)
ICAO: CYRT
In our report I provided some insight in one of the replies that might help you diagnose the issue.
@matheof reported SKLT, which I tried to spawn at as well with no success.
It happens with the base airports or with the addons available in the marketplace.