When the spreadplayers command is used in a function that is part of the load or tick tags and if the target player in in a dimension other than the overworld the player has a large chance that they will be teleported up in the air or into a block.
The glitch also occurs if the command is in a function called by a function in the tick or load tags but not when the function is called manually by a player.

Original description:

When ever I use spreadplayers in a function with the tick tag or a function called by the ticking function it can teleport me into a wall or in mid air. The same command will not do this when typed in chat.
I've attached the datapack where this is happening below for easier testing.
You can type this command to reset yourself and make it teleport you agian
/tag @s remove nthstInt
Edit: The bug also appears when the command is called from a function in the load tag and only occurs when the target player is in the nether or end dimensions.