Leads are not rendered correctly on all types of walls.

I think this is the same as a bug report from 4 years ago that I have included the link for but that was closed ever a year ago because it could not be duplicated, and it is still an issue. Simply attach a mob with a lead to a wall (not one of the ends of the wall) and there is what appears to be z-fighting.

https://bugs.mojang.com/browse/MCPE-15036