Following on from Waitaki, the reason why the Z axis homes then lifts and homes again is so that the second homing can be done slower and therefore more accurately. The distance it lifts is customisable in firmware. If it is not lifting enough to release the switch, you should change the setting in firmware to make the lift distance higher.
If you are using Marlin look for this in configuration_adv.h:
//homing hits the endstop, then retracts by this distance, before it tries to slowly bump again:
#define X_HOME_RETRACT_MM 5
#define Y_HOME_RETRACT_MM 5
#define Z_HOME_RETRACT_MM 4
There will probably be similar in other firmwares.
My Z home retract was originally 1mm and did not work reliably. 4mm works fine for my mech endstops.
If you are using Marlin look for this in configuration_adv.h:
//homing hits the endstop, then retracts by this distance, before it tries to slowly bump again:
#define X_HOME_RETRACT_MM 5
#define Y_HOME_RETRACT_MM 5
#define Z_HOME_RETRACT_MM 4
There will probably be similar in other firmwares.
My Z home retract was originally 1mm and did not work reliably. 4mm works fine for my mech endstops.