I would strongly recommend unchecking the ambush flag on your item spawns. It doesn't serve the same role as it does with standard ring or monitor objects; it makes it so that items automatically disappear over time, and it makes it so that the respawn timer for each spawn isn't dependent on when the item disappears. This means that all of your items are disappearing at once, and they're all respawning at once. Each spawn produces particle effects, so this produces a lot of momentary lag at the point of spawning.