I absolutely have no idea how to reproduce this but that's not the first time i notice this ...

I had a Unbreaking III Efficiency V DIamond Pickaxe (i also had the same bug with the same enchants on a Diamond Shovel) that broke (i check it twice in the inventory the last time it happens, it was gone, and i was pretty mad about it as it was unintentionnal ) then i threw a few ender pearl to go back to my base as it started to becom dark (i dont know if it matters but i threw one in water)

Arriving at my base i was surprised to see the Pickaxe back in my item bar (i'm also pretty sure i was full on my way back to my base, and the slot was used by some crap, mushroom if i recall and that item was gone)

Thats not the kind of bug i'll look to reproduce (as i dont want to lose those kind of item in survival), but as i said it was not the first time i noticed this behaviour.

If it happens again another time i'll try to gather even more details ...