Duplication or disappearance at the edges of chunks

Blocks can disappear or be "duplicated" when they travel through different chunks.

Here, another piston head is created. But if it's the redstone block that moves between 2 chunks, it will sometimes disappear. These are not ghost blocks.

To reproduce, build that kind of clock, and unload and reload the chunks. You may get this. I got it several times at the same spot.

A possible important thing to say : these 2 chunks were in my spawn chunks before I changed them by /setworldspawn somewhere else. But they weren't the edges of spawn chunks, or lazy chunks. (This is happening after the change)