Why the bedrock doesn't work "@s" on Command Block?

Note: I am bad grammar for english, because im deaf, please read.

Bugs:

I try to write the command block...

I want to make "@s", like a self (private player), i dont want @p!

If you write /effect @s levitation 3 3 you dont have the effect nothing! Please fix that.

I have recording and watch here, please.

Click here in my video: https://youtu.be/p5_fCTBY2PY