Good find @Esther! I’ve reproduced this and sent on the info. It has to do with the grappling hook being selected in the inventory. If something else is selected in the inventory, the grappling hook would work normally, but when it’s selected in the inventory, you can make it use three hooks when it shouldn’t.I'm not sure if this is intended, but my topaz hook can grapple 3 blocks at once.
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I also think I should note that I also have a normal grappling hook equipped.