I've died twice when this issue occurred when i died where i had a wolf backpack and when i got back to all my things it was a standard & empty backpack, the second time a creeper exploded behind me and i had the rare bat backpack of which i found in a mine-shaft and again when i returned it was an empty plain backpack if i catch this again on video, hopefully it doesn't happen again but still, I will attach the video file.