pocketmine in server-side is applying the cooldown to the items with the same stateId, while through PlayerStartItemCooldownPacket the cooldown is applied to all items with the same name.

This means for example that for example when using a goat horn, the server is applying cooldown to an specific variant of the item, while the client is applying cooldown for all goat horns.

So we have a mismatch here.

Also i'm not sure if vanilla sends PlayerStartItemCooldownPacket to tell clients about cooldown.

Also i'm not sure if vanilla sends PlayerStartItemCooldownPacket to tell clients about cooldown.

From my tests in BDS vanilla sends PlayerStartItemCooldownPacket for all new items that have cooldown (shields and goat hoarns). However, it doesn't send this packet for old items that were added back in MCPE days (chorus fruits and ender pearls). They have their cooldown implemented client-side. I think we can skip this and send the packet for all items?

pocketmine in server-side is applying the cooldown to the items with the same stateId, while through PlayerStartItemCooldownPacket the cooldown is applied to all items with the same name.

This means for example that for example when using a goat horn, the server is applying cooldown to an specific variant of the item, while the client is applying cooldown for all goat horns.

So we have a mismatch here.

It looks like vanilla bothers only about item type. Would it be correct to change the logic in pocketmine to use typeId to store cooldown?

There's no direct link between PM item types and Minecraft item IDs. In some cases multiple IDs are flattened under the same item in PM, and in other cases a single ID is split into several PM-side items. Basically you can't rely on either typeID or stateID for this.

Possibly a better approach might be to introduce a "cooldown tag". PM would start a cooldown using the item's cooldown tag if it has one. Then any other items with the same cooldown tag can't be used until the cooldown expires.