Having trouble to level you freshly assembled 3D-printer top section?

Here we need the gantry plane to be flat, some variances can make it unheaven :

-Bad assembly

-Floor plane unheaven

-Flexibility of the frame

-A mix of all the previous points

What is the gantry plane ? : The plane created by the upper extrusions where the rails are moving

This plane is composed by 4 segments, which lead to a potential imprecision

Most of the time caused by a bad assambly, the floor can by beeing unheaven inducing a flex in the machine frame, leading this place to be more like a curve

A X crossbar with flatness issues on a curve will create a more complex curve with sometimes strange topology, even with perfectly flattened bed. This issue is not a bed issue, it is a gantry flatness issue. Your probe is measuring the bed, but reversly probe the gantry flatness too.

This issue can induce a premature failing of the rails since we place too more tension in them, this can lead to unheaven motion resistance in Core XY based machine, especially on large ones

You need a cheap laser-leveler with eventually a tripod or any holdind solution you prefer (not included in this kit) in addition to 5x of thos pine with 5x M3x30 and a hammer nut matching your frame

The manual can be found here