Derelict Mansion bosses doesn´t drop any loot

Have had this happen to me twice now. Killed the bosses more or at the same time and doesn´t drop any loot. Have had similar bug happen with other bosses that appear as a pair. The Twin Millers, Pitlord and his skeleton mammoth. Feels really bad when you´ve put a lot of time and then risk jucing out the map just to not receive any rewards.