Items that do not stack randomly despawn in Minecraft.

This is vanilla Minecraft in version 1.16.4, I've tried this in the nether as well as well as with other items, and this does not change. Additionally, if I throw down stackable items with non stackable items, a lot of stackable items before they stack, or full stacks of stackable items, then the same. I have not tested this in other versions, but it did also happen in Optifine 1.16.4 HD U G5. This does not happen in survival.

Video: https://www.youtube.com/watch?v=vgWok1HCAwg