Space map. 1 friendly npc group. 3 enemy npc groups (used in mission objective). The enemies, of course, appear when the objective becomes active.
When these groups start fighting, after a few seconds, some npcs will randomly teleport far away. In my case, they are teleporting just to the edge of the planet, which is placed map center (so maybe they are "trying" to get to 0,0,0). I only found them because I followed the friendlies to their location after the non-teleporting ones were defeated.
I ruled out that it's being caused by any sort of animation (like quirky "warp in" effects). I also tried setting a patrol route but that didn't stop them from teleporting.
This can be REALLY annoying when testing a map. In my case, some of the enemy NPCs would spawn INSIDE the planet. If they were more than 10km deep my only option was to use the editor Kill command to allow the story to progress.