Mod version: goblintraders-1.6.0-1.16.3
Forge version: 36.2.2
Minecraft version: 1.16.5

I'm experiencing a strange issue, I found a goblin trader in a cave, and decided to capture one and bring them home, I put a name tag on them, and tied them to a fence using a lead in my house temporarily on my staircase.

Something strange happened shortly after, when I tried to move them as they were awkwardly in the path of the stairs, it's like their hitbox is gone, I can still trade with them, but they don't move, they can't be pushed, and even they don't fall when blocks under them are removed. They're completely frozen, immovable, and defy gravity.

Possible replication method:
To recount exactly what I did, I brought them out of the cave, temporarily threw them in a hole to make a staircase up the mountain to my home, brought them up, tied them momentarily to the fence of my farm, they didn't freeze when tied there, I went to check in my house for where to put them, decided the staircase, untied them from the farm and then moved them to the staircase rails. Not sure if this helps but that's what I did.

What mod allows you to tie them up with a lead?