Hi there, 

Muitiple times I have (3 times) I found that my minecartt with hopper just disappears. 
Maybe it falls out the world border or something maybe, I don't know.. 
I have a creeper farm, and the ever moving hopper minecart just disappeared. I didn't break it, nor touch it... 

the same thing used to happen with tridents and now I'm not sure if that's fixed or not.