The case of the missing panzer

So I'm just playing a game of origins about to get the ice Staff and I see if I can find the part for the maxis drone in the excavation site, and then out of nowhere a panzer spawns in. This first time I take it out. This was weird because it was very late and it should have came a couple rounds ago. One round later in the same area a panzer spawns and downs me. I kill it and setup again and then finally about two rounds later 2 panzers spawn in a kill me. What the heck is going on? Why did it not spawn til I opened excavation site?