Summary:
Items appear to desync while they sit on a block that is moving, (look at [the video showcasing it|https://www.youtube.com/watch?v=55zhEylDTS4&ab_channel] to be clear, THIS IS NOT THE SAME ISSUE AS MC-4 as in the video shows, its not that outside of the block to cause by it self, what mc-4 is. Also, (although the video doesnt show) if the machine were to stop, the desync stops 

Reloadding may make the item jump and let it fall

Steps to reproduce: 

1) build the atached clock with the trapdoor setup
2) run the following command: /execute positioned [position at trapdoor] align xyz run summon item ~-0.1 ~0.5 ~0.2 {Item:{id:"minecraft:diamond",count:1b}}

3) notice that the item ends up "falling" yet is not consistently doing it. After falling it ends up on the block up again