When y'all try to change the items on a Grenadier wearing predator armour (so they have three slots in total), does the item selection window bug out and go blank? It's been repeatable for me--the only fix is to back up there (into a busted equipment window) and click the half-visible item button, which will fix the display and let you select your item like normal.
It's a bug as I've seen it in Christopher Odds playthrough, hopefully it'll get patched out soon. Also on the same playthrough he recruited an extra Reaper through a covert op while his original was still with us so it may be possible to grind out a full squad, it'd take a while though!