Procedure to select random player returns null entity for no reason

I made a procedure that uses the "for each player in the current world as entity iterator" block to make a procedure that randomly selects one player in the world by assigning a random number to each player and picking the player with the highest number (by progressively comparing them until only the highest number remains). This is the procedure. It worked seemingly fine when I tested it, but for some reason, if you leave the world and rejoin, when you try to use it again, the first time it works fine and then the second time it returns a null entity. I can't figure out why.