Here are fixes I tried :
- Adding a big collision under the spawner
- Teleporting the NPC in a loop (doesn’t seem to do anything)
- Raising the spawner height so that the internal system has time to correct the issue (even after 10s the NPC is still falling)
When it randomly happens you either want to kill the NPC and spawn it again, or, since it seem to only happen when you try to spawn the NPC right after teleporting the player somewhere, adding a sleep before spawning the NPC seem to fix it (for me)
EDIT: The issue depends on the player, some players will never make it occur while others might always make it happen