I am running a push pull system. I have my two motors in series they are both bondetech extruder drives with exactly the same ratio. I had tried hooking both drives to seperate drivers on the duetwifi and i used mixing extruder in my case 1:1 ratio it worked but amount of filament used on the DWC was way off basically if the part required 10 meters of filament dwc would say it had used 20 meters of filament. My suggestion to you is to use identical extruder drives with and hook them up in series...I keep the one closest to the extruder fairly tight and the push drive a bit on the loose side.....I have never had a problem with missmatch between the two drives....I have done prints in excess of 40hrs

I have a new housing design for the filament monitor if you wish to try it. It doesn't take long to print
and so far has been consistent on the filaments that I have tried.
https://www.thingiverse.com/thing:3219410

One other thing that I noticed on the image is that the bed does not seem to be level this can also appear to be under extruding. If you look at the left side of the image the lines seem to be joining however on the right side the lines are not joining. This may indicate a none level build platform. The other item that you have to look at is the start height of the print. If the nozzle is too far away from the platform it will also appear to be under extruding at the plastic will not be squished and will appear narrow. This also looks like the first few layers of print. What happens if you complete this test cube. Does the infill get better as more layers get printed?

I use Borosilicate Glass (I use this to prevent bed warpage) with buildtak flex system. I use hairspray on the buildtak as PETG tends to stick too well. Bed temperature of 80-90 and nozzle temp 240. NO COOLING FAN. As people have mentioned in the post not all filament is the same. Be also careful of the layer heights and the larger layer heights and print widths can also cause larger shrinkage and cause some warping. Lower layer heights give the part a chance to relax between layers.
My build surface is 300 x 600 and i have done prints to almost full bed size with PETG...

I had the same issues with the corners. Tried everything the same as you did. This is how I resolved it noting that I was using Simplify 3d slicer to as my slicer. I was about to give up however I went to the Kissslicer and download Kisslicer and set it up almost to the default except for the printer hardware. Low and behold the corner blobs went away.. ok so what is the difference. I compared the settings of both slicers and discovered that Kisslicer printed perimeters Outside in . I had simplify 3d set to inside out as recommended almost everywhere. Once I changed to outside in the issues went away. Change all the pressure advance, retract, additional advance to 0 and the slowly recalibrate those settings. Just do one at a time in very small increments. I now have almost perfect parts.

There is a stepper motor calculator that can be found at https://daycounter.com/Calculators/Stepper-Motor-Calculator.phtml if you fill in all the information you will get a theoretical max speed that you can drive the motor. I did a simple check using information provided for stepper motors from (stepperonline.com) using the following motors (nema 17 17HS16-2004D 45Ncm) and (nema 23 23HS20-2004S 90Ncm) you will see that the calculator outputs the results Nema 17 max speed max speed 11.6rev sec and the nema 23 max speed 6 rev sec. It is not just the inertia but also the induction that plays with the max speed a stepper can move. If for example you were to change the induction on the Nema 17 motor from 2.6mh to 5mh you will see that the Nema 17 motor would now only have a max speed of 6 rev sec. I hope this helps a bit

The remaining filament shows N/A however the paneldue shows time remaining
I am wondering if it is because I am using 2 drives for the extruder ( The filament is quite far from the pinter and I had discover that 2 drives prevents any issues ( I had put the drives in series however now I am using 2 separate drives mapped as below
M584 X3:4 Y0 Z2:1 E5:6 ; Apply custom drive mapping

Are you printing on bare aluminum?
If you are that may be a problem try covering with Kapton tape and using hair spray it works wonders
I too tried cast aluminum plate with the same result I ended up switching to Borosilicate glass and my problems with leveling went away

What hardware changes are required in order to run SBC build of RRF for Duet 2

One other note that I forgot to mention. The filament amount is displayed when I initially start the print however it is depleted about halfway through the print and that is when this issues as explained come up

I have built a 60cm x 30cm printer about 8 yrs ago and have gone through all the trials and errors in order for it to be successful.
I started with a large cast aluminum build plate.(cast aluminum is known for dimensional stability and is used in precision fixturing.) While heating this plate it would deform and i had a huge problem keeping it level. The next phase was to use borosilicate glass. This solved the problem of deformation during heating and the plate stayed level. I use 2 lead screws for the Z axis and i do a bed level before every print. Keep the x y as light as possible as this is where the effects of weight will slow down the printing. I use a direct drive extruder and my print speed is restricted to around 60mm second. Travel speed is around 90mm sec. Although it is not a speed demon it works for me. I have explored the use of closed loop steppers and have found out that i can increase the speed slightly but in the long run it is not work the complexity at this time. I have performed prints that have duration of mor than 4 days printing time without issues.

they work great.....i have one using it on an tenslog idex pringer

I have the same setup and the same issue
If you wire up both SCRs in parallel then each heater element is not closed loop
I just ensure that the Start GCODE starts both heaters and end GCODE shuts off both heaters
M104 P0 S<TEMP>; set bed 0 temp
M104 P1 S<TEMP>; set bed 1 temp

There are two things that will cause this

1. Nozzle too close to the build plate... Print first layer and measure layer to make sure that the layer is actually the right thickness...if first lay is to be .3mm then the first layer print should also be 3mm.
   This may also be a bed level problem
2. Over extrusion... this can happen if you have if you have adjusted first layer extrusion width to be more than 100%

Just and additional thought
I would put the microscope so you can see if the belt is repeatable this will rule out backlash. it is is not repeatbable do the same with the motor to see if that is repeatable. I do know if you are stopping on a microstep this may not be repeatable

Are you using Bang Bang heater control or PID
A long time ago i was using BANG BANG and i put a indicator on the platform and i could see movment in the platform of up to .2mm. I changed to PID and that variation went away..you can use PID with SSR without a problem.
Also if i were you i would use a seperate power supply for the DUET controller and one for the bed heater that should control your 24vdc variations. (Personally i would use mains to power a bed heater but that means purchasing a new heater)
One other thing that i noticed was the way you are pulling the filament off the spool. With that arrangement you are going to be twisting the filament. This may cause issues with the extruder.

Check out the M82 M83 issue
I recently had the same issue and i was pulling out my hair
Ensure that your slicer is not inserting M82 or M83 someplace it shouldnt
I found my issuer on my Z homing file that i had written years ago

@jrjones88
There are a couple of items that can be causing this

1. Check to insure that the extruder and hot end are not moving or loose. If it is loose then may get something that looks like your print
2. Even though you are not hearing any clicking on the extruder the filament may not be feeding smoothly. Is this a bowden type extruser or direct Drive?
   If it is a bowden extruder try squirting some light oil in the bowden extruder to help eleviate some of the friction.
   Also clean out the nozzle as sometimes there are some small chunks in the nozzle that block the filament from extruding smoothly
   Check the actual filament drive as I have had issues where there was a string that was wedging against the filament and causing inconsistant extrusion
3. The extruder is too cold. When going up in nozzle size you may have to increase the temperature for the highter volume. Try 10 or 15 degrees higher and see if it helps

@docfail
I use kisslicer, superslicer, simplify3d all the instructions are in mosaic support area
each of the slicers have there own issues so its what works best for you

What Errors are you getting
I used this setup without issue
Also octoprint is not too friendly making the connection to Duet