PLAYING IN REALMS, SURVIVAL, WITH EXPERIMENTAL GAMEPLAY ON - NOT SURE IF IT AFFECTS SINGLE PLAYER WORLDS, 

Anyways, I was playing on a realm, not created by me, and was the only person on.

Outside my base, was a wandering villager, standing completely still, with no llamas.

I tried to open his trading GUI, which didn't work - and I tried multiple times.

After I tried multiple times, I punched him with my bare fist, and he skyrocketed up into the sky.

Update:

The other realms players and I have come across the frozen wandering trader three times now, standing still roughly above our underground base. All the times, the trader had no trading GUI, and he levitated if you pushed him off a block, and flung into the air when he was hit...