Items disappear from hoppers when loading/unloading chunks.

Items in hoppers are disappearing when loading/unloading chunks. Tested multiple times. Noticed because I was using a 4 minute hopper clock and had to refill it twice when returning from the nether and noticed the machine no longer ran.

 

This does not appear to happen everytime. I will randomly notice the machine stop working and find no items in the 2 hoppers facing each other.

 

Works fine if you don't leave the chunk for extended afk sessions.