BL touch Mysrtery Problem

Hello there fellow printermans

Many days now im trying to figure out an issue with bl touch.Z axis moves( like it's trying to level the bed) while i print but it doesnt get it right.In some corners of the bed surface,nozzle prints to low and vice versa.
I tried M48 and results are okay and the X axis is almost perfectly calibrated. At cura i use the M29 after M28.Also i tried M420 and there was no difference. Except that i haven't done any changes at cura's g.code.
My printer is the Ender 3 pro with btt skr V2.0 and i use bl touch smart 3.1. I have tried many marlin versions but the problem remains.

For the love of god help me.
Thanx

I placed my M420 in Cura's Startup G-Code adding it to the very last line.

M420 S1 ; Bed Leveling On

I used m420 after m28 and m29 , not at the very end of the code. I will try again tho i,thank you.
Plus i will add the z offset number with the z offset wizard of Merlin. i had it zero untill now ( like the most of YouTubers ) . I hope this make the difference.

Btw do you know how the " fade " and "mesh" can affect the print ? There are some standard values for this characteristics?
At one forum i saw that if you have warped bed its good to set the "fade " value between 15-20. Is that right ?