In this lesson I encountered the same bug as Ayeng_AE mentioned, when this happens the InventoryItem gameObject becomes parented to the Stats Canvas and when you go to hide the Inventory Panel the InventoryItems that are now parented to the Canvas remain visible. From what I understand is that you parent to the canvas temporarily in order to be able to drag the item around the whole screen but is there a way to also save the original Inventory Slot parent so that it returns to being a child of one of those?
Optionally would there be a way to break out of all this if the left mouse is already dragging something and the right mouse is clicked everything just goes back to how it was?
https://imgur.com/ymUZfRi < shows objects new parent and “floating” potion/hammer