Marlin Error On Rumba

Hello everyone! I am having a little trouble with Marlin on my Prusa I3V 12"
Essentially I have been reuploading the Marlin software to calibrate my new double extruder. It seems as though firmware artifacts have remained on the board after the numerous re-uploads of the Marlin software, causing unexpected results.First: the G29(Auto bed level) stopped working, then the homing (G28) command made the Z move up instead of down.
Any help is greatly appreciated.

It sounds more like mis-configuration rather than firmware artefacts remaining. Are you sure you haven't reversed the Z axis travel direction in the firmware? Check your configuration.h for where the Z axis travel direction is defined (inverted or not) and for where auto bed levelling is enabled.

Search for
#define INVERT_Z_DIR

and for
#define ENABLE_AUTO_BED_LEVELING

Thanks for your answer!