Allay left the lead by itself

I originally bolted it to the fence today but the allay pictured left Leash Knot on its own and I didn't notice how it became this way.
Now this allay is dragging a rope on its body, but can fly around freely. I noticed that this rope probably has collision volume, although it sometimes gets caught in the cube. And I can't remove this rope from it.

Just like the second picture, I bolted 4 Allay on these 2 fences.These four allay were all here, but when I looked back was to find them all off the leash, I do not know what happened

Quit and re-enter the game make the rope on it disappear,but I still can't tie the rope for this allay