I have made and imported worlds onto realms and turned NPC spawning off, with the same issue persisting once these worlds are downloaded into single player as well so it seems to not be a realms issue.

With NPC spawning turned off, wandering traders naturally do not spawn, however the game tries spawning them regardless which leads to trader llamas spawning without their respective trader. Since they are not on a lead, they do not despawn and act like regular extremely out of place llamas. This can be a nuisance in a creative world as you have to deal with them whenever they spawn.

How to recreate:

• Create a world with NPC spawning turned off.
• Wait the required time for a wandering trader to spawn.

(Note about screenshot: game is completely unmodded, the white bricks are from a resource pack)