Two reasons come to mind. First is that you don’t have the micro-stepping in the stepper driver set correctly. If you started from the V1 maintain firmware and are using either TMC2209 or the DRV8825 drivers, then your micro-stepping should be setup correctly. If you are using some other driver, then you should verify that micro-stepping is set correctly. Depending on the driver, it should be set to either 16 micro-steps, or 32 micro-steps.
If the micro-stepping is okay, the next thing is to check how the steps per mm is setup. Using a connected computer, or if you have a TFT display in the console, enter:
M92
this will give your steps per mm for each driver. If your driver has 16 micro-steps, then you should get the values (100,100,400,100). If your driver has 32 micro-steps, you should get double that value:
(200,200,800,200).
Steps per mm can be changed in two ways. It can be done in g-code:
M92 Z400
M500
The M500 save the result to the EEPROM.
Second, If you never used an M92, then you can edit the values and reflash the firmware. In configuration.h, see this line:
#define DEFAULT_AXIS_STEPS_PER_UNIT { 200, 200, 800, 200 }
if you already send an M92 to set the steps per mm, then changing the firmware will not change the values unless you do a M502 (factory reset) first.