Then try to spawn option. Perhaps once hidden the ai might unposses the character. Then when it “awakens” it may not be possessed again. Also could intersection with the terrain cause them to get stuck?
If the phantoms repeat at the same places try raising them slightly above the terrain and see if that helps
also try do debug the AI with the " key
See if the phantom AI is possessed and if it is running any types of behaviors
Edit: pressing the " key in front of an AI will set it the the current debugged character.