z axis homing issue

I have an i3 prusa variant printer with a z homing issue at start of print that I have not been able to solve. When I start the print it homes the z axis then raises again a few mm (hot end temp check i think) but does not come back down far enough to engage the z endstop before starting the print. It's always about 1mm high. It causes adhesion issues to the bed. I can still print, with issues...

The stepper motors are fine, it is not missing steps that I can tell. There are no issues with the couplings between the z motors and the 5mm threaded rods, everything is snug.I am using slic3r 1.29 to generate gcode. Slic3r has the standard G28 ; home all axes G1 Z5 F5000 ; lift nozzle in the start gcode section which is a default setting as I understand. Slic3r's z offeset is set to zero.

My marlin configuration_adv has these settings

#define X_HOME_BUMP_MM 5
#define Y_HOME_BUMP_MM 5
#define Z_HOME_BUMP_MM 3
#define HOMING_BUMP_DIVISOR {2, 2, 4} // Re-Bump Speed Divisor (Divides the Homing Feedrate)

Marlin version is 1.10 RC6. Does anyone know what I should do to fix this?

did you figure this out? i am having almost the same issue where z axis will go home, raise up a little and grind for some odd reason then go a little higher then start the print.

Z max feed rate in firmware is to high.

homing rates are slower and thus work

ie #define DEFAULT_MAX_FEEDRATE {300, 300, 5, 25} // (mm/sec) needs to be
#define DEFAULT_MAX_FEEDRATE {300, 300, 3, 25} // (mm/sec)

some machines need 2...