Server lag caused with mere 30 units. Fabbers had an area reclaim command which they couldn't reach. This resulted in as much as 5-7ms Task Plan cost PER UNIT! Works the same with area assist and blocked pathing. (Already aborted and reassigned the job when I took the screenshot, but reissuing it still caused Task Plan phase to jump back up to 80ms/frame. Was as bad as 120ms/frame before.) Second screenshot is for comparison after all fabbers have aborted their job. Notice how Task Plan went down to 1-2ms with ~200 T1 tanks patrolling full planet?
