I'm playing Immortal Empires, started the save yesterday, using patch 2.1.0.
I'm Heralds of Ariel and just settled Fort Soll (the Empire Fort just south of Pfeildorf). The settlement chain however has only corruption and growth related buffs, but no garrison whatsoever. None of the 5 tiers.
1) Star a campaign as Heralds of Ariel (I'm on easy/easy)
2) Occupy Fort Soll with a force
3) Check the garrison details/building chain
I own all three games and all DLC and FLC.
I'm running the game with two mods, which both aren't the cause of this, "One Button Respec" and "Recruit Defeated Legendary Lords". Added my modified log as requested, and a saving showing the problem. See also the screenshot below.