I think too, it is related to the networkcode. Why should especially that code be the only thing in the software that is workling as it should?
For a mis.file size of 800kb it takes me about 45 sec to join as client, for a 1MB mis.file size +20minutes. And it doesn´t matter if the map has only spawnpoints on it or 15000 stationary objects, the AI planes, vessels etc disappear randomly at some time, some do not even spawn visably (we have external views on for testing, so you can switch to an airplane or vessel but you don´t see it). The size of the formation doesn´t matter too, even single planes or ships dissappear, and if they do not dissappear I see them flying sideways or backwards, even with a ping of 35. The skript doesn´t matter either, cause when you spawn the AI directly without script, they disappear sooner or later too. Hosting the same map on a non-dedicated server, I have no problems with the AI.