Before the Zann Invasion I completed the quest where I have to talk to "man in strange black armor" who gives you the quest to go to Zann outpost where you then search for a missing Zann caravan. After completing the quest you're given a token which let's you recruit higher tiered troops from the Zann Oupost captain. However there seems to be a bug where when he asks you for food, you have the same 2 responses repeated (so you now have 4 options, with the bottom 2 being for the elite tiered troops). The text options should be changed instead of accepting or denying the food it should just be something like 1) "I wish to recruit basic tiered troops" 2) (After completing the quest mentioned above) "Here is the token granted to me from <I forgot the black armored guy's name>. I wish to recruit your elite troops". 3) "Sorry, I'll be off".
Also, after you recruit troops, if you talk to the captain again, you'll have the same text options, but you won't be able to actually recruit anyone for some time.