You’re spawning the characters in a spherical random location, thus you’re getting random values in Y as well. Guessing you have at least one clone that spawns below the floor ever so slightly.
You could try grabbing the Y position of your current player and explicitly overriding the Y with the position of the main character and then combining that with the X and Z values of the random position.
If your landscape is not flat within the specified radius of your random sphere location you would then need to figure out the proper height at whatever distance from your player character will be otherwise it will still fall through the floor.