#define MOTORS \

so the correct setting is #define XAXIS_STEPS_PER_MM 2048

#define XAXIS_STEPS_PER_MM 10240

At first this is what I had: #define DECOUPLING_TEST_MAX_HOLD_VARIANCE 20  // I increased this to 40 

#define EXT0_MAX_FEEDRATE 100

#define HOST_RESCUE 1

#define EXT0_INVERSE 1

#define EXT0_ENABLE_PIN ORIG_E0_ENABLE_PIN

#define BLUETOOTH_SERIAL  -1

#define Z_PROBE_PIN

#define NONSTANDARD_SDSS

It seems that even though it has #define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 4000, 500 } in my firmware, at some point a M92 command was issued and I guess followed by a M500 (to make it stick). 

* #define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 4000, 500 }

To test I downloaded the latest version of V2 and I only changed "default_envs = RUMBA32" in plaformio.ini and "#define MOTHERBOARD MOTHERBOARD_RUMBA32" in Configuration.h

#define min_software_endstop_x true

#define MULTI_ZENDSTOP_HOMING 0

#define EEPROM_MODE 0

#define CONFIGURATION_H

#define DEBUG_MOVES

#define ENDSTOP_X_BACK_ON_HOME 2