Some of my items disappeared (not despawn)

I've been playing on a world for a few months now trying to gather all the achievements I can (not relevant). I was fighting zombies in a spawner room trying to repair my mending armor when I wasn't paying attention and died. This location was right underneath where I'd respawn. When I got to it all of my items were there except my netherite helmet (enchanted to the brim) and a stack of potatoes which weren't that important. I have no idea where it went. I even dug a 25x25 block area around where I died and couldn't find it. Could someone explain this?