When the /clear command is put in a repeating command block to clear a player of a specific item, and /replaceitem in a chain command block forces the same item in a specific spot in their inventory, it freezes their entire inventory. They cannot remove or add any different items. Both commands work exactly as they should on their own, but not together. The idea is to simulate the Curse of Binding enchant, since it isn't present in the game yet.