So far I found 3 monster zoos, cleared all of them and none of them rewarded any loot. Also ammo recovery seems to be broken in monster zoos as I must have shot atleast 20 bolts with maxed out Crossbow skill and failed to recover any.
Well, it wont reward if he had found the zoo and then left either the floor or to the pocket dimension. He does have to at least have found the monster zoo before it will do this. Or at least that is how it always worked, it is possible that a bug crept up in the wizardlands I guess. No one else has mentioned a bug like that though.
I have had the same bug since adding Wizardlands. I cleared multiple zoos without leaving the floor or going to the pocket dimension and haven't received a single reward.
Have you checked your inventory? Lately I've noticed that monster zoo rewards don't pop-up anymore, but I still get the rewards for clearing it.
did you actually follow the counter under the map? Sometimes random monsters in rooms near the zoo get called 'part of the zoo' and you have to kill them (even though no knockback, etc. is happening). And at least once I never did find the last monster - I even checked all the walls to see if any were destructible.