After a good amount of attempts, we finally brought down the Ogre boss, but I didn't get a weapon/armor drop.
Everyone else got 1 to 2 pieces of armor (no guns), and all I got was 1 Mouldering Shard.
This was the first time any of us got armor/weapons (except me) from the whole raid so far with the exception of 2 people getting the Ghost from the prior boss.
Are these bosses not guaranteed to drop weapons/armor?
The user below is correct. It is all based on RNG. However, the moldering shards you collect through the raid increase the chance of you getting a drop. The more you collect, the more likely you are to get an item.