If you were to run this kind command for example: execute if entity @s[gamemode=survival] run say test

this would work, but when you try to use @s with a selector argument to run a function, the function fails to run.

Like for example execute if entity @s[scores={Data=0} run function code:players/

You will see that it absolutely does nothing, not even tell you a failure. I'm thinking that this bug existed ever since 1.13 due to the command system being rewritten. This most definitely is a bug because this would work in 1.12 but not work in 1.13+.