I managed to get purges till lvl 8, this last one killed my rhino (xerxes, r.i.p. it was with me from 3 years or more). The spawn problem still occurs but more is now rare. Maybe some data was saved after a successfull spawn, who know, but now they learned the way, the main problem stills the demolishers that 1hit everything, mobs that pass through doors, when the stygian commander challenges you, the hordes keep coming, and it can be a very painful due to demolishers, and at high lvl purges they over crowd your fight with the commander. High risk, low rewards, purge lvl 5-7 stills more profitable i did 9-10 on single player and the rewards not improved so much. Maybe increasing he drop rate for advanced warfare components, and recipes and schematics and archer posts do the purge more profitable.