Fixing Lag Issues in a Map

I'm currently working on a spawn-based map. Everything is working just fine, except for one thing. Every time any unit engages in combat, the map starts lagging severely. The map doesn't contain too many doodads, units, or triggers, and the size of the map itself is only "Large". Does anyone know what the problem is and what I could do to fix it?

Only when a unit starts engaging in combat? Do you have any triggers that deals with that, because otherwise people can't find or see what's wrong with that description.