With a mending tool in hand or in the offhand, it hardly ever gains any durability (unclear under what conditions it does, other than a grindstone - might be only when fishing and the rod with mending took no damage from unbreaking, and the random chance of application triggered), while when using a grindstone (which autopickup doesn't gather the orbs for), the item gains a huge percentage of durability.

A good resolution would be to make sure this works for the 1.16 method of all xp going to mending items first. An ideal solution would be to somehow ensure all normal XP pickup events are resolved as normal.