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 ...
Duplicate of MC-1040 - If you have not , please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.