Playing in the offline mode. I created a portal to a Swamp Provisioner realm, with the focus of obtaining the schematics sold by the trader within. Every time I approach the location on the map, I see the traders name/title, and then the proceed to fall through the map. I am unable to reach them before this occurs. Making it impossible to trade.
I have tried closing and reopening a portal, closing and reopening the game, but nothing seems to work.
Stumbled onto the same issue in a Herbarium Swamp today. It seems the NPC location was just under the ground level. He was in that location until I was 50m away. At that time he fell through the world.
Possible solution = Move the NPC spawn point 2-5 meters up.