I am not an expert in C# but maybe it is worth trying to do actor removal in the main script like
onActorCreated
timeout 180mins
destroy
It is done this way on Repka1. Check out the script in the mission
http://forum.1cpublishing.eu/showpos...5&postcount=44
I may guess that the code you posted destroys aircrafts not only once in 3 hours but every 3 hours... and if you load this code with every submission and if you have many submissions... there will be many pieces of code active that destroy aircraft every 3 hour. Many airgroups will be destroyed resulting in disappearing dots. Make sure all your airgroups have a landing waypoint in the end to prevent them from disappearing in the air.
Do you experience ghost planes on the server in the 1st 3 hours into the mission?