Hej dear dev,
I found a bug while playing Minecraft Java edition in 1.16.2. I place a fence (spruce) near another two other ones (I was placing the corner fence) while a chicken evade and accidentally goes at the exact same spot I was placing the block. I ended up with two other weird fences (they hitboxes where similar to the visual aspect). I had to break and replace the block to update them again.
I hope you may easily find where the issue come from and that this issue is not a duplicate.
I link some pictures.