Had a Law Domain cleric who had a negative DEX modifier. After reaching level 4, I had him gain the feat "Might of the Iron Legion" which is supposed to give some weapon proficiencies - which it did - in addition to heavy armor proficiency. I was in the middle of the Dark Tower when I leveled up so I only noticed that I didn't get the proficiency when I eventually stumbled upon some lootable chain mail. Since the heavy armor proficiency is arguably the biggest draw of the feat, this should probably get fixed.
According this wiki https://solastacrownofthemagister.wiki.fextralife.com/Might+of+the+Iron+Legion
it's only supposed to work on fighter, paladin and rogue. I just tried it on a wizard and got the same result, no heavy armor proficiency. Luckily I saved right before.
Maybe I missed something but don't all fighters and paladins have all those proficiencies by default..? So really it's only there for Rogues that don't want to stealth.
I ran into the same issue yesterday, v.0.4.21 - Public
they should code it so that it des not even present as an option, for an ineligible class.