I had this problem as well, i'm not really sure how I fixed it but I know it had something to do with the drive settings in your firmware.

This is my config:

; Drives
M569 P0 S1                                 	; Drive 0 goes forwards
M569 P1 S1                                 	; Drive 1 goes forwards
M569 P2 S0                                 	; Drive 2 goes backwards
M569 P3 S1                                 	; Drive 3 goes forwards
M350 X16 Y16 Z16 E16 I1                    	; Configure microstepping with interpolation
M92 X100 Y100 Z1600 E95                		; Set steps per mm 
M566 X1200 Y1200 Z4.5 E300                 	; Set maximum instantaneous speed changes (mm/min)
M203 X24000 Y24000 Z120 E3000              	; Set maximum speeds (mm/min)
M201 X1000 Y1000 Z100 E5000               	; Set accelerations (mm/s^2)
M204 P400 T400                            	; Lower accelerations when printing though
M906 X750 Y750 Z750 E750                   	; Set motor currents (mA)
M84 S0                                     	; Disable motor idle current reduction

I am having some struggles with under extrusion on my Anet A8 so I wouldn't copy the E values.
I also changed my leadscrews to some with a lower leadscrew pitch, so the steps per mm for the standard rods should be 400.

Glad I could help

So i'm getting 100 mm of extrusion when extruding at very low speeds, when I move to higher speeds it extrudes between 10 and 20 mm of filament. I had the steps per mm at 105.2 before but I changed it back because I didn't know if it was correct or not.

I already changed the heater block, nozzle and throat, and after that is still happens. So I don't think that's it.
pretty sure my nozzle height is good.

So i'm having some issues with my Anet A8 under extruding (I think).
The top layer has these weird gaps between 2 lines. It didn't do this before I got a duet so i'm pretty sure its firmware or software related but I just can't figure out what it is.

This is my config.g file:

; Configuration file for Duet WiFi (firmware version 1.20 or newer)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool on Wed Jun 06 2018 12:53:11 GMT+0200 (W. Europe Daylight Time)

; General preferences
G21 						; Work in millimetres
G90                                       	; Send absolute coordinates...
M83                                        	; ...but relative extruder moves
M555 P2 				  	; Set firmware compatibility to look like Marlin

; Network
M550 PMy printer                           	; Set machine name
M552 S1                                    	; Enable network
M586 P0 S1                                 	; Enable HTTP
M586 P1 S0                                 	; Disable FTP
M586 P2 S0                                 	; Disable Telnet

; Drives
M569 P0 S1                                 	; Drive 0 goes forwards
M569 P1 S1                                 	; Drive 1 goes forwards
M569 P2 S0                                 	; Drive 2 goes backwards
M569 P3 S1                                 	; Drive 3 goes forwards
M350 X16 Y16 Z16 E16 I1                    	; Configure microstepping with interpolation
M92 X100 Y100 Z1600 E95                		; Set steps per mm 
M566 X1200 Y1200 Z4.5 E300                 	; Set maximum instantaneous speed changes (mm/min)
M203 X24000 Y24000 Z120 E3000              	; Set maximum speeds (mm/min)
M201 X1000 Y1000 Z100 E5000               	; Set accelerations (mm/s^2)
M204 P400 T400                            	; Lower accelerations when printing though
M906 X750 Y750 Z750 E750                   	; Set motor currents (mA)
M84 S0                                     	; Disable motor idle current reduction

; Axis Limits
M208 X-36 Y-8 Z0 S1                        	; Set axis minima
M208 X230 Y219 Z230 S0                     	; Set axis maxima

; Endstops
M574 X1 Y1 S0                              	; Set active low endstops

; Z-Probe
M574 Z2 S2                                 	; Set endstops controlled by probe
M558 P7 i1 H5 F120 T6000                   	; Set Z probe type to modulated and the dive height + speeds
G31 P500 X-26 Y-40 Z0.625                    	; Set Z probe trigger value, offset and trigger height
M557 X20:200 Y20:170 S20                   	; Define mesh grid

; Heaters
M305 P0 T100000 B4138 C0 R4700             	; Set thermistor + ADC parameters for heater 0
M143 H0 S120                               	; Set temperature limit for heater 0 to 120C
M305 P1 T100000 B4138 C0 R4700             	; Set thermistor + ADC parameters for heater 1
M143 H1 S280                               	; Set temperature limit for heater 1 to 280C

; Fans
M106 P0 S0 I0 F500 H-1                     	; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off

; Tools
M563 P0 D0 H1                              	; Define tool 0
G10 P0 X0 Y0 Z0                            	; Set tool 0 axis offsets
G10 P0 R0 S0                               	; Set initial tool 0 active and standby temperatures to 0C
M200 D1.75

I did notice some clicking noise and inconsistent extrusion when extruding at higher speeds, while at lower speeds it extrudes fine.

Any help would be appreciated

Glad I could help

This is my config:

; Drives
M569 P0 S1                                 	; Drive 0 goes forwards
M569 P1 S1                                 	; Drive 1 goes forwards
M569 P2 S0                                 	; Drive 2 goes backwards
M569 P3 S1                                 	; Drive 3 goes forwards
M350 X16 Y16 Z16 E16 I1                    	; Configure microstepping with interpolation
M92 X100 Y100 Z1600 E95                		; Set steps per mm 
M566 X1200 Y1200 Z4.5 E300                 	; Set maximum instantaneous speed changes (mm/min)
M203 X24000 Y24000 Z120 E3000              	; Set maximum speeds (mm/min)
M201 X1000 Y1000 Z100 E5000               	; Set accelerations (mm/s^2)
M204 P400 T400                            	; Lower accelerations when printing though
M906 X750 Y750 Z750 E750                   	; Set motor currents (mA)
M84 S0                                     	; Disable motor idle current reduction

I am having some struggles with under extrusion on my Anet A8 so I wouldn't copy the E values.
I also changed my leadscrews to some with a lower leadscrew pitch, so the steps per mm for the standard rods should be 400.

I had this problem as well, i'm not really sure how I fixed it but I know it had something to do with the drive settings in your firmware.