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 !!

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 ?

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 !!!

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.

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.

Maybe this can save somebody else a few hours of frustration ....
I have been printing with PETG on a particular printer and was having all kinds of print quality issues. The print was overall ok but the detail was terrible with lots of cleanup required. More cleanup than the usual PETG issues. Holes and voids were the biggest problems with the inside dimension being too small. Stringing seemed to be more than usual as well.
I tweaked all kinds of settings without success. In frustration, I finally took the filament spool off the printer and installed it on another printer and ran the same print - it came out beautiful.
I had eliminated the filament and most settings as being the culprit.
I decided to look at the nozzle in some detail thinking that maybe it had worn oversized or maybe there were other issues. When I unscrewed the nozzle, there was no initial 'break' as the nozzle started to turn which to me indicated that it wasn't totally tight. I cleaned out the nozzle (propane torch treatment) and re-installed. A new print resulted in the problem printer printing as clean as it did on the previous test printer!
The moral of the story - an imperceptible wiggling of the nozzle caused me a LOT of grief! While it is also possible that the nozzle had some sort of partial internal obstruction that was cleared out in the torch treatment, I believe that all my problems were related to the lack of proper tightening of the nozzle.
An important detail - I run a Dragon hot end on this printer. In the Dragon, the nozzle does not seat against the heat break like it does on most regular hot ends. A regular hot end also generally uses an aluminum heat block which expands when heated, this would cause all kinds of oozing of filament out the top and bottom of the heat block and the problem would be immediately obvious. A regular hot end must be hot-tightened because of that.
The Dragon uses a copper the block which does not expand anywhere close to an aluminum block and hot tightening is not required.
Anyway, I thought I would share the lesson I have learned over way too many hours!

This aught to be interesting: ) I got the popcorn, a glass of cool liquid and am ready for the entertainment

@chrishamm WOOOHOOOO !!!! We are back in business .... thank you very much!
BTW, the 'turn off everything' command works - thanks for fixing that!

A related question - I just ordered a 3.3V regulator for another project and noted that most of these surface mount regulators self limit on current and temperature. Would it be safe to assume that the 12V regulator in question would just limit the output current for the brief time required for the fan to start up (this shouldn't affect the fan itself in any way) or are there other considerations I am forgetting about ?

@mrehorstdmd, no problem, thank!

@dc42, thanks. I am set up for 400 steps/mm but that is a good thing to keep in the back of my mind (where it will probably get lost among clutter and cobwebs
Other people might find this tidbit of info interesting too.

@mrehorstdmd, do you happen to have a source from Aliexpress for the magnetic tape you used?

I am happy to report that with a tighter S parameter the G30 command does in fact probe multiple times like it is supposed to. Doing a repeatability test with 10 measuring points yields a deviation from mean of 0.003 with the maximum deviation being +0.005 and -0.004. This is with an 'S' parameter of 0.005.
I think I had a maximum S deviation set to 0.01 because a tighter setting did not allow my bed scanning macro to complete. I have yet to re-do a bed map to verify that 0.005 for S will work.
I will need to make sure the homez.g macro only runs after the bed has reached operating temperature.
Thank you for all your help!

@Phaedrux, good question - I don't think so but life has gotten in the way of running tests. Maybe I will have a chance tomorrow.

@engikeneer, yup, that is it! I turned support off and PrusaSlicer gives me 139 layers in the preview. The option to synchronize is only available if the top contact z distance is zero.
Well that clears up that mystery .... thank you very much!

@OwenD, thanks ... I will play a bit with things tomorrow.

@moth4017, thank you for your suggestion. My config.g contains the following line for the probe:
M558 P9 C"^zprobe.in" H3 F60 T6000 A10 R1.25 S0.01 B0. I will try to switch the B0 to B1 to turn off the heat to see if that improves things. I will also reduce the S parameter to S0.005 and see what happens.
I had actually forgotten about this configuration setting and had not noticed any repeat probing action during the G30 command. With a reduced S parameter it should become clearer if the printer is verifying z zero with more than just one measuring attempt.

I have a small model that I am currently working with. I have set layer height to 0.1 mm and have not enabled variable layer height. In Prusa 2.6 alpha 5 the model shows as being 189 layers high. The overall model height is 14 mm so the Duet web interface tells me it should take 140 layers. The same model in PrusaSlicer 2.6 alpha 4 shows 211 layers in the preview.
PrusaSlicer 2.5 generates 139 layers for the same model as it should seeing the first layer is 0.2mm.
So, is this happening because 2.6 is an alpha build or does 2.6 do something weird and fancy which results in the extra layers being generated ?