What’s this for you:
Perhaps when the world shifts, it wipes the player via Kill Z (could work in both directions - untested) before their position is adjusted. That’d be a weird bug, though.
Adjust the number and see if you’re getting a different result.
when my character flies above 10485 meters
This kind of adds up, you can’t spawn actors beyond 1m uus, and float precision is really poor at that distance. Consider having the World Origin Shift kick in much, much earlier.