Watch the video. When trying to take items out of a chest that is constantly being cloned it is very difficult as often the items will glitch back into the chest. In the video the tick delay of the command block was 0 or technically 1. Whenever you try to take an item out the exact moment the command block ticks and clones the chest it will glitch it back into the chest. One simple way to get around this is to simply increase the tick delay, but it still happens occasionally. This is super annoying when I am playing on somebodies pvp world, and it takes me 30 seconds to take a single item out of the chest as it keeps going back in from the bug. This problem only gets worse with ping and lag.