@T3P3Tony, Thank you for keeping the forum. Discord has it's place but loosing the forum would be very bad IMHO. I agree with your two reasons to resist a move to Discord. I do utilize Discord but it is another tool and another approach at a community but should never be considered as a replacement.
Thank you for all your hard work!!!

Hope you are all having a very happy Christmas (or whatever else you celebrate). Stay safe !!

A special THANK YOU to everybody at the DUET team for your incredible service both in the design and especially the support !!

Steppers are current based devices. Although general specs usually list a voltage, it is irrelevant for your purposes. When a stepper driver switches on a phase, it measures the current that is drawn by the motor and limits that current.
Since the phases of a stepper motors are coils of wire, they have inductance (which is also listed in the spec's). When you switch on current to an inductor, the current flowing will not go to full current flow but rather the current increases at a given rate based on inductance and voltage. In order to increase speed, you need to be able to bring the current up to the rated current as fast as possible. Higher supply voltage will do that for you. A 12V power supply will supply the same rated current but will not do it as quickly.
Since a stepper motor works by switching on (and off) current in two windings, a higher voltage can substantially increase your speed.
If you ever look at the speed vs torque curve on a stepper, you will see that torque decreases very quickly as the motor speed goes up. This is simply because the drivers can not supply instant current and it takes longer for the current to reach the rated current if the voltage is lower. So, if you happen to trip over a graph plotting torque vs rpm at different supply voltages, you will see that a higher voltage power supply keeps the motor torque higher at a higher motor speed (because rated current is reached quicker).
A side note - the maximum torque a motor can develop is based on it's construction and current handling capability but there is a given maximum. Torque will basically remain at that maximum until the on/of/on switching of phases gets too fast (net current through the coils is reduced because it takes a finite time to go from no torque to full torque). A higher voltage power supply can force the current to rated current faster than a lower voltage power supply.

Not everything in that rambling reply might be correct but the overall gist is correct.

I just finished a test print with 100% success. Thanks for the suggestions.
I think the major problem was that I never removed the gap from when I was printing both the model and support with pla. I had completely forgotten about this.
I also printed slower although I don't actually know which of the many speeds is used - I suspect it was 26 mm/sec for petg and pla at 40 mm/sec.
The petg and pla stuck together to a limited degree ... enough to hold everything together yet not so much as to make support removal difficult.

I only have two words ...... Woooooo Hoooooo !

@alankilian, I REALLY appreciate any and all help and I apologize if you felt in any way slighted whatsoever. It was most certainly not my intent !!!
I got confused by the sentence "The point of continue is to skip an iteration."
DanS79 cleared it up and confirmed my interpretation by saying "To be clear it doesn't skip an iteration, it skips everything after the continue statement in the current iteration." IE it doesn't skip an iteration but goes back to the beginning of the loop.
Your example (thanks) did however clarify another point on the continue command that I was not aware of and hence my earlier confusion about sequential 'if' statements. The iteration happens over the 'while' loop and not as I had assumed over the 'if' loop. A very important bit of learning for me!
So to repeat, I apologize profusely and hope we are back on the same wavelength !

Moderators .... could we please lock this thread and stop with the negativity please ?

Wow, what a ride ..... I am happy (more like ecstatic) to report that after correcting my config.g (thanks again @gloomyandy ) the printer completed both a pressure advance test and a temperature tower without any complications whatsoever !
I did an M122 Bnn and nothing seemed out of the ordinary ... but then the prints came out just fine so there shouldn't have been anything odd to report.

If your offset values are zero, you are probing points that the Duet doesn't know about and you are then taking those probing points to adjust the mesh height. You are creating a bad height map and then applying it.
I don't understand how you can possibly expect any results but crap. You might as well work without any height map.
It's odd that you get stripes but before anyone can give you any suggestions about what is wrong, you MUST set things up properly !!!

I am happy to report that the issue seems fixed. The printer has been going for a bit over an hour and nothing untoward has happened (knock on wood). Hopefully it's because I replaced the connector rather than just having moved things a bit and re-establishing a good connection.
I can't believe that the first connector I replaced was the dud one - I fully expected to replace each and every connector with the last one being the problem ....

It amazes me how quickly things went from a bit of a jumpy temperature graph to a single heater fault to 8 or so faults on my last print.

BTW, for a 215C set point, the temperature fluctuates between roughly 214 to 216 with the vast majority being between 214.8 and 215.4.

Another method that is often used with CNC mills is to allow the switch to be bypassed. Instead of the carriage directly activating the end switch, the switch is mounted to the side and a lever is used to activate it. The carriage approaches the lever and depresses it which activates the end stop switch but there is no hard stop so if it takes a mm for the carriage to stop, nothing is harmed.
You could use a micro switch with a lever with a roller on the end and have a protrusion on the carriage that activates the lever without running into a stop.
Hard to explain but very simple and effective.

Just as an additional thought - how about mounting the extruders on a single plate with a swivel point in the middle. The idea is when one nozzle goes down, the second one goes up ... and vice versa. I am pretty sure that I have seen this kind of arrangement in a commercial setup before but I have no clue where I saw it. It was quite a while ago. The point being that you save some weight.

@3DPrintingWorld, 'spiking' would imply 'going high'. A short would not do that.
If this is just a terminology issue and you are referring to a temperature DROP then I would look at two aspects. How is the heater connected to the Duet? Are you using any connectors or is the only connector at the PCB. I have had many issues with connections overheating causing poor connection which then causes heating which then causes even more issues. Look at all connections to make sure the contacts are not discoloured.
I have also run into 'gentle' temperature dropping which can be caused by a defective thermistor. Rapid changes (ie instantaneous) could indicate a bad connection someplace since the hot end can not change instantaneously.
A defective thermistor might also cause sharp drops.
I have seen a number of issues and most of them relate to either the thermistor or bad connections on either the thermistor or the heater.

@Crosswire, don't know if it is related but on occasion I also get a blank page. It resolves itself quickly (might take 2 or 3 reloads). Today I had a blank page that did not resolve itself but I had no trouble with the same page on another computer (it was already loaded).

@MJLew, thanks again for your suggestions. This morning I collected the new print and there was only a tiny area that showed the same symptoms as the earlier print. It was a thing of (mostly) beauty!
I do not know what parameter change(s) caused the huge improvement. I forgot to mention that I had also added a tiny bit of support but that support was not in the problem areas but rather what PS felt strongly about.
I need one more of these fittings so I will get to reverse one or two of the previous changes to maybe narrow things down a bit more but my gut feeling is that reducing the speed was the cause of the improvement.
The next print will be started tonight for another overnight print.

@MJLew, thanks for the input. I have rotated the print and reduced the speed from 180 t0 100 mm/sec and started another print. It is a 6 hr print so it will be a while before I can see if there is a difference.
In retrospect, while PS does indeed slow down for bridges, I am not entirely sure this applies to overhangs in this part. Looking at the speed as reported by PS, it seems there was no slowdown. On the other hand, the overhang test sample did show a drastic speed reduction for the very outside filament laid down. It should be interesting to see how this next print turns out.

I am trying to print a 4 inch sch 40 45 degree pipe fitting. The fitting is printed with one open end flat on the build plate. Since this is a 45 degree fitting, I was under the impression that the most overhang I would encounter would be 45 degrees. Well this seems to not be correct for some reason or other that I don't really understand. I get severe artifacts on what I would think are the highest overhang portions.
I test-printed an overhang test piece with the chosen settings using PrusaSlicer and there was no distortion on the highest angled overhang which was 70 degrees (PS automatically reduces speed and turns the part cooling fan to 100%)
I also tried slicing the part with different settings of maximum overhang to see where PS started inserting supports and that happened at 75 degrees approximately.
I have a number of questions:
Since this fitting is a 45 degree fitting of a 4" pipe, are there actual sections where the overhang is more than 45 degrees?
Is there any other way that I can print this part without using a huge amount of support material? I tried different print orientations but that didn't get me that far.
Attached are a couple of photos of the artifact which to me look like a case of not enough cooling (I printed at 205C with PLA) but printing the overhang calibration print showed no difference between 205C and 195C.

@Phaedrux .... or turn the part cooling fan off during the first layer
My next job that requires weight is actually going to be done with sand and I will try to remember to turn the fan off.

@dlc60, I suspect that my closing the web control window and opening a new window does exactly the same thing that you accomplished by clearing your cache and cookies ..... but hey, it's a computer so what do I know
There is no question in my mind that there is a gremlin in the DWC system somewhere ......

I have a similar issue with a Duet2 WIFI and a Duet3 6HC. In my case, DWC slows down to unacceptable levels after having been run for a while (several days). In my case closing the DWC window and re-starting the web access brings speed back to normal.
This has been an issue for a very long time which has been reported in the past but no cause/fix was ever found. I have learned to live with it

@Phaedrux, while not impossible, I don't really know what I am doing. Could you give me a hint as to what you expect to see? There is no apparent (at least to me) difference in printer behaviour between a printer that shows hiccups vs one that doesn't produce hiccups. I don't know if maybe one would see choppy motion for example ... but there is no hint of choppiness.