Z jumps running manual bed leveling

Hi all

I have a RAMPS1.4 running Marlin-MPCNC_Ramps_T8_16T_LCD_32step_DualEndstop
I uncommented the manual mesh bed leveling and set it to a grid of 4x4

However I get a jump of about 5 mmm in z height 3 quarters along the y axis, at every point across the x axis, coming back in drops down.

I’ve played with using the g29 s3 to make a mesh
test 1. 4x4 grid
high (8mm) Y to low (0mm) Y
test 2. 4x4 grid
high (8mm) X to low (0mm) X
both work with smooth transitions.

However with my correct mesh loaded and the maximum different only 2mm it jumps.

Any ideas?

I raised an issue on the Marlin github page but I need to be running marlin bugfix 2.0

Oh what joy trying to get it working.
I have all axis working but autohoming move the wrong axis and then crashes Marlin.

So I have marlin-bugfix.2.x installed and working on my SKR1.3 with dual end stops.

However bed leveling will not work on my 2440x1220 bed size.
If the bed size is 600x600 then my mesh (would) work. however when the bed is configured with the correct 2440x1220 and the mesh loaded. at about 900mm the z axis jumps up, and down on the return.

ANYONE HELP!

That’s really strange. I would ask the question in the Marlin support, although they get really swamped with issues.