I'm new at speedrunning this game and i don't understand all the things. Can someone can explain why on 4-2 and after performing the 3-bump method, the screen sometimes scroll to the right when taking the pipe (which disable the wrong warp) ?

I don't know how to explain why, but if you stop on the pipe, then press down, it should work.

if the screen is moving to the rigth just at the moment (frame) that you enter, it continue scrolling
you have to enter when the screen is absolutely entirely stoped to dont move it more, rigth?

You should come to a complete stop before entering the pipe, otherwise, the screen tries to catch up to Mario's position. It's important to make sure you are completely stationary before you try and enter the pipe.

Kosmic's sub-5 tutorial should help: The part about the wrong warp starts at 10:20

I started speedrun this because of this video especially. Anyway thanks for the help everybody