Found it.
Seems I have to set also U and V to 0 reference after a Z probe.
Now it works.
macro calibrate Z max for each axis:
M208 S1 Z-3; Allow z to be negative
G90;
G1 X0 Y0 F10000; go to the center
G1 Z30 F1000;
G30 ; probe bed and set z=0
G32 ; start 3 point bed leveling
G1 X0 Y0 F10000;
G30 ; Probe for Z=0
G1 Z10 F800 ; raise nozzle
M584 Z6 U8 V7 P5 ; split z axis
G92 U10 V10; set U V axis to 10 as Z
G91 ; relative mode
G1 H3 Z370 U370 V370 F1000; move Z, U, V down until endstops trigger and get new z limits
M500 P31 ; save new z height
M584 Z6:8:7 P3 ; unsplit z axis
G90
Have to say, object models and conditionnal gcode is a killer feature. 🙂