If a player has dropped items, a large amount of blocks in the area could cause them to disapear no matter what they are.

How the bug happened(for me): during a fight with a wither i had died a few times being unprepared but when it was over i was missing many items from my inventory including netherite items. Searching for them was met with nothing.

How to replicate (not tested): drop a specific item such as a sword, then drop lots of blocks nearby in a way where they dont cluster into singular piles. The sword or any other items may disappear when theres a large number of blocks on the ground