My item Was gone or Despair When I die

I was killed by a endermen on my underground base and then after that 3x I was just dead by endermen or kill by enderman and when I back were I just die and then my item was despair or gone I don't know that was a bug or just a normal and my drop item was despair I don't know how or were my item go I just know I have one left item or 3 left item I had