I have experienced this already a multiple times after death in the Overworld.

All dropped Items and Experience Points disappear after death even though they are actually here. 

Sometimes they only get invisible and can be still picked up when walking over the spot where they normally would be but sometimes they disappear completely and the game/save must be restarted multiple times until it is loaded and shown again at all. sometimes they appear shortly just to be visible for a few seconds when loading the game but disappear quickly again.

Screenshots:

I died there 2 times in a row with items in hand and couldnt get them to appear after respawning. Restarting the game or reloading the save state didnt do anything. Edit: They reappeared now visually, but can´t be picked up.