I was told this is not a traffic rather an airport issue.
Told by who ?
The gates at the airports are obviously correct and perfectly lined up as they should be. If they weren't, this couldn't possibly happening:
When I start the flightsimulator and the traffic spawns in, everything is perfectly fine.
A parking spot in the airport scenery file is either correctly placed and correctly lined up, or it's not. If it's not, it would appear regardless if the AI just spawned or they are arriving after a while, the position set is always one and the same so, clearly, this cannot possibly be a problem of the airport, according to your report of traffic spawning correctly, so it must be a problem of the AI engine of the sim.
Just to be sure, have you disabled the Microsoft Zurich scenery ? Even if you don't see visual issues, there's still might be a scenery conflict which might cause issues with AI in general.