This has happened a couple of times now.
Get full on inventory. Go to merchant stall to sell off stuff, summon merchant. May have happened many times I didn’t know a person was supposed to come until I saw this.
Then later, another time.
Nothing too different, just a different spot in the floor.
What I couldn’t capture in a screen shot, was when I closed out of the vendor sell window and had unloaded a few items, the merchant seemed to ‘run’ through the air from the spot in the ground toward the stall.
Maybe they are just appearing on the wrong vertical axis level near the stall and I’m not watching the animation or aware of what it is supposed to be? She doesn’t seem to stay stuck in the floor eternally.