Alien Hunters - Berserker boss not appearing

[Padishar]

I am playing a v1.5 LW2 campaign with no other mods, Veteran difficulty. I have both AH and SLG activated, and got their initial missions pretty early in the campaign. I beat the Viper King in the second encounter as he appeared quite shortly after he escaped in the Nest mission. I don't remember the game month I killed the Viper King in, but now I am playing September, and still haven't seen the Berserker boss. Regular berserkers have appeared every now and then for quite a long time. I've not skipped any particular mission types either. I have done supply raids, all kind of GOPS, liberated regions, defended haven attacks, and even got one invasion. The most advanced alien opponent I've thus far encountered is Archon (just a few, and very rarely).

When am I supposed to be encountering the Berserker queen?

[Dwarfling]

Try Facilities. I think the rulers guard those now. Also I remember seeing them before in Troop Columns.

[Padishar]

I have two facility leads, but should there be some facilities in the map before it's worth researching them? Avatar project is also at 0 pips thanks to completing a couple of golden path objectives and liberation of multiple regions. The Avatar progress is slowed down a lot due to the amount of missions I have been able to complete.

I had a troop column mission yesterday, but no berserker queen. I'm currently infiltrating a UFO mission and a Supply Raid, so I'll see what happens the next time I launch the game. I was wondering if there was some mechanism slowing down the appearance of the alien rulers, or if they are scripted to always start appearing a bit after the previous one got dealt with. Does anyone know about it?

[Padishar]

Finally she appeared. September 22nd, so it was quite easy to take out right away with coil weapons and lucky Ionic axe throw stunning her.