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.
The other coordinates default to the execution context, which is the spawn point (from chat, it's your position). You'll have to add different ones to the selector if you want to do that