When closing a chest inventory, and opening a chest inventory in the same tick, the InventoryClickEvent is never fired when clicking on any of the slots.

I know that this is a problem with Spigot, because if I delay the exact code by one tick, it works just fine.

Why would you open a new chest inventory the same tick as closing one? I would use this when chest inventories are following up after each other. E.g. in a shop there would be a confirm chest inventory.