I have not fully diagnosed the problem but here is the main issue I see so far,

execute as @a[y=-1024,dy=256,tag=!in_void] run tellraw @s "Welcome to the VOID"
execute as @a[y=-1024,dy=256,tag=!in_void] run tag @s add in_void

If you run something like this (In our case referencing outside normal world bounds) within a datapack for some reason it does not run these commands (It also does not output any issues with them when loaded in) and if you put a say command it will successfully hit that part of the mcfunction.

You can manually copy these commands into the game and they appear to run correctly.