Certain characters can't loot Chain Mail Armor by clicking "Loot All" and instead it remains on the corpse.

Lurgan (Duergar) has a suit of Chain Mail Armor on his body but when my Ranger character looted his corpse; she looted everything EXCEPT the Chain Mail Armor. I then tried looting the corpse with other characters and I found out that only Lae'zel was able to grab the armor automatically. The only other option to get the armor was to manually drag the armor into your inventory.

I had the same issue where both my Ranger character as well as Gale can't loot "Scale Mail Armor" either when using "Loot All" yet Shadowheart and Lae'zel have no problem looting those.

As such it seems that "Loot All" is bugged as characters will apparently only loot armor from bodies if they are proficient in that armor or something. If they are not the armor is left on the body; potentially causing you to miss out on it.