Hoppers not working

Whenever I put items in hoppers the items disappear after moving to a new hopper beside it a few times, or after a while, not under, and the comparators next to the hoppers don't update until you break them and place them back down. My adventure map is not working because of all this, and it is getting extremely annoying! PLEASE fix it! This is the most important problem I'm having in Minecraft right now!