Here's a first:

Today for the first time including years of Bnet before resurrection
Had

Andariel in Hell (Doesn't matter which difficulty) drop NOTHING no potions scrolls no junk or items of any kind. It's never happened to me before I was under the impression Act bosses had to drop something be it junk items like scrolls or items

She probably died on a spot where the map doesn't allow items to drop, essentially casting the items into the void. The most classic example of this is when when you kill ghosts off-platform in

Arcane Sanctuary, but it can happen in lots of indoor areas - like in areas with graves in the floor (like in

The Forgotten Tower), if a ghost dies on top of that there will be no drops.
As for

Catacombs Level 4, I think (but I'm not 100% sure) that there are "dead" drop areas around the pillars. Maybe someone else knows more specifically. You're not the first to encounter this anyway.

This situation happen to me in

Baal once. I cant believe that when it happen.

There is no chance of getting 100% nothing. There is always something, if nothing but the tp scroll, identifying scoll, gem(s) etc.
The loot just spawned elsewhere and made it seem like boss drop nothing.

a lot of times they just drop some

Gold lol, and I go thanks, you bastard.
it's like such disrespect, you kill them and he drops some coins like "here you go, dog"
mepho/diablo/

Baal hell lol.