Leads vanish when transporting leashed entities through a Nether portal

The bug

When transporting a leashed mob through a Nether portal, the lead vanishes completely as soon as the mob is teleported.

This issue does not appear to be present in Vanilla 1.15.2.

To reproduce

1. Build a Nether portal
2. Spawn a cow
3. Leash it
4. Lead it through the portal
   → As soon as the cow is teleported, the lead vanishes
5. Go through the portal into the Nether
   → The lead is not there either

Video

Minecraft 1.15.2 - Multiplayer (3rd-party) 2020-03-22 13-09-23.mp4