The axolotl closest to the crosshair in the screenshot remains connected to the lead in the player's hand despite the incredible distance between it and the player.

How to recreate:

Create a very high column of water as shown (this one is ~60 blocks). Carry an axolotl via lead into the sky, away from the column. This was done with 2 axolotls simultaneously, in creative mode.

Lead the axolotl towards the column and position the player a few blocks higher than the water column, but also a few blocks away horizontally. Use space and shift to vary the player's y-coordinate between ~2 blocks below the top of the water and ~5 blocks above the top, occasionally flying horizontally over the water.

As the bound animal swings around, it should enter the water and try to swim, but its momentum keeps it swinging around and attached (most of the time; see below).

Unintended result:

The first hanging axolotl was able to free itself and fall down into the water, snapping the lead in the process. The second axolotl also fell in the same way as the first, but the lead did not snap and stretched as the axolotl descended to the ground level.

As can be seen in the first screenshot, the lead continues to exist without snapping even though the axolotl being dozens of blocks from the player. Note that the axolotl is walking along the ground.

Terminating the result:

The second screenshot shows that the phantom lead persisted, even after switching to other items in the hotbar. It finally ceased to exist after applying a fitting name tag on the axolotl.

Other notes:

This was reproduced on 2021-02-16 at 23:52:57 UTC with 5 axolotls simultaneously, and one of the self-freed axolotls remained frozen ~5 blocks from the top of the water column inside of it, and it did not move until another axolotl freed itself and collided with it.