When pressing any button in an existing world, one of my friends teleports 1000 blocks each second (went to 30000 blocks but could go farther with more testing) while under the bedrock layer and is unable to move. If it were survival he dies (___ fell out of the world) and cannot respawn. Happened on a realm and a copy of that realm in 1.16. Was unable to join a week before 1.17 released and now having this unique situation. Occurs to him on both iOS and android devices (linked to his account specifically). Please get this fixed as soon as possible!

Specifics:  This occurs in the overworld. He was invisible to other players when he spawned, was underwater, and in a ladder. Was in a world created on 1.16.  Error message after dying and trying to respawn: "Disconnected from server". Unable to rejoin world from the main menu after dying. Most likely teleports the second he would die from falling out of the world in survival. Tends to teleport 1000 blocks in the positive direction of the x-axis. Cannot move while teleporting. When I teleported him to me using commands it did not step his teleportation under bedrock. Only happened in this world and copies of this world (from 1.16) and only with this account after 1.17. Will test to see if he is having trouble with worlds created before 1.17, but right now he is able to join worlds created in 1.17. Realm is currently on 1.17.1 (due to Switch release). The world has been in survival for its entirety and only tested in creative for a copy of the world. No other accounts from iOS, Windows 10, or Nintendo Switch are having any issues. If you need to know the account just ask. Will send screenshots and videos as soon as possible. Please fix!