So, all was going just fine, but then, I arrived in the sewers. I played a little bit, but I had to quit, so I saved, and, well, I quit the game to do what I had to do then. When I came back, though, I killed some drowners, and after trying to loot them, I realized that they had nothing. The game acted just fine, though, except I couldn't press "Take all". I passed on, but I had the same problem with a quest object: the cockatrice head. It didn't appear at all in the loot menu. Curious, I checked some barrel, and they had the same issue: no loot, yet the game acted like they did contain stuff. I carried on, killed bandits, searched them, just in case, and they DID possess something... It was a strange... Well, entity, named Natural Weapon, it didn't have any graphics, just a black square with letters and numbers on it. I couldn't pick it up, I couldn't equip it: nothing. Sadly, I didn't take a screenshot. I loaded a previous save, far back in the game, and tried to loot something: same problem.
TL;DR: no loot appears, quest item or not, then black box with weird stuff appears.
Any idea on what to do?