I haven't tested this much, but I'm playing on a server and I tied like 5 leads fence-to-fence and after a while it just disappeared. However when a mob was tied to a fence using lead it stayed there for weeks, so I assume Quark's feature is bugged.

It disappears if you unload the chunk, but not the node on the fence. If you want to break it, it doesn't drop the lead.
Minecraft: 1.16.4
Forge: 35.1.36

Dupe of #2641