This bug report is for elite version. I think this new difficulty setting got leaked into standard elite version when Elite plus is released. Earlier, there was only one set of apex adds spawning as long as one of them is alive. At the moment theres a second set spawning even if 1st set is alive. Btw we did not burn first apex add group at all. So theres no reason for second set to spawn.
Yea maybe try 5 Tanks then. Just kidding. The first boss is insane anyway... alot of work to do there.