Tail and gills of an invisible axolotl don't render when viewed from certain angles

The tail and gills of an axolotl will not render when viewed in spectator mode, or when the entity is on the same team as the player. This behavior is especially unusual for the axolotl, considering it's arms (which are also 2D planes) are visible from the top and bottom of the entity.

Steps to Reproduce:

1. Spawn an axolotl

2. Make it invisible
   

   /effect give @e minecraft:invisibility infinite

3. Change gamemode to spectator

Observed Behavior:

The tail will not be visible when looking at the axolotl from it's left-hand side, and the gills will not be visible when viewed from the back.

Expected Result:

The tail and gills would be visible at all times, regardless of the entity's effects, or the gamemode the player is in.

Fix:

One possible fix is to copy the texture of the 2D plane to the opposite side (similar to the feet currently). This does cause z-fighting though, likely due to another underlying issue.