When making a collection system for a mob farm with minecarts, I found this bug. I found a perfect hopper minecart unloader design and tried it on singleplayer. It worked. However, when testing on a multiplayer server, the minecart would get to the hopper, but the hopper wouldn't take any items. This ruined the system. Even when i simply threw an item into the hopper, it didnt pick it up. If this was a problem with the redstone, it would've not worked on single player as well. I'm not sure why the hoppers are acting this why and request help if I'm making a mistake or if this is a bug. I don't believe it's a problem with the server, as other hoppers have worked before in fishing farms.