It appears that the level 5 item in all professions do not reward experience. My guess is that the developers expected the target item to be crafted for gold replenishment (other items may be more profitable).
Several other items, notably consumables like potions, provide more/less XP than their 'neighbors' on the list. Again, it seems to be biased around the marketability of the item.
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https://www.arcgames.com/en/forums/neverwinter#/discussion/1244763/armorsmithing-bronze-helm-no-armorsmithing-experience
It appears that the level 5 item in all professions do not reward experience. My guess is that the developers expected the target item to be crafted for gold replenishment (other items may be more profitable).
Several other items, notably consumables like potions, provide more/less XP than their 'neighbors' on the list. Again, it seems to be biased around the marketability of the item.