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.
Please check if that's still an issue for you in the latest 1.14 (pre-)release.