It is likely the same issue as in the dragon rescue and why you sometimes see floating weapons.
The monsters the generals summon are spawning with full sets of gear attached to them. This causes the lag I believe. Turning the armor to wardrobe only lowers the lag a lot but will cause the monsters to bug out randomly and spawn with their mesh hidden, so you only see the weapons floating there.
I'll see if I can stagger the summons to not spawn all at once.