Here is the config.g file. I'm not an expert, but it looks like the motor currents are set to 800ma and the idle currents are set at 30%.
Those figures would seem to be pretty close to normal.
The Z axis acceleration is set for 250 mm^2. Maybe that is too fast?
After some searching, I found the specs for the stepper motors, and the max current is 1.7 amps, so it looks like I could bump the motor current up, to maybe 1200 ma?
; Configuration file for Duet Ethernet (firmware version 1.21)
; executed by the firmware on start-up
; generated by RepRapFirmware Configuration Tool on Sat Feb 09 2019 18:14:01 GMT-0500 (Eastern Standard Time)
; General preferences
G90 ; Send absolute coordinates...
M83 ; ...but relative extruder moves
M667 S1 ; Select CoreXY mode
M550 PHypercube EVO ; Set machine name
M552 P0.0.0.0 S1 ; Enable network and acquire dynamic address via DHCP
M586 P0 S1 ; Enable HTTP
M586 P1 S0 ; Disable FTP
M586 P2 S0 ; Disable Telnet
M569 P0 S1 ; Drive 0 goes forwards
M569 P1 S1 ; Drive 1 goes forwards
M569 P2 S1 ; Drive 2 goes forwards
M569 P3 S1 ; Drive 3 goes forwards
M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
M92 X80 Y80 Z4000 E420 ; Set steps per mm
M566 X900 Y900 Z12 E120 ; Set maximum instantaneous speed changes (mm/min)
M203 X6000 Y6000 Z180 E1200 ; Set maximum speeds (mm/min)
M201 X500 Y20 Z250 E250 ; Set accelerations (mm/s^2)
M906 X800 Y800 Z800 E800 I30 ; Set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout
; Axis Limits
M208 X0 Y0 Z0 S1 ; Set axis minima
M208 X300 Y300 Z300 S0 ; Set axis maxima
M574 X1 Y1 S1 ; Set active high endstops