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.
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[Mod] OcelotOnesie
migrated
The ticket was closed because it had not been updated in over a year. I have reopened the ticket.