If it were me, though, I would rewind with bobstro and pay special attention to his advice on LiveZ.  Even if the unit is a year old, get the printer working as if it were "newly build" - then customize and tweak. 

I ONLY run with 7x7 bed leveling. As I have mentioned before, quality is more important than speed. I will almost always side with quality.

I am having a problem getting Octoprint to work (and I posted for help on this). So I am using an SD card.

I have done Live-Z adjustments. I had thought (perhaps incorrectly) that I was dialed in correctly. Any higher and I had unattached strings. The height I had was (perhaps incorrectly) working for all of my other prints with good adhesion to the bed and a smooth surface on top of the first layer. You felt otherwise, and that I was too close to the bed. You may be correct, but when I moved the nozzle up I was back to unattached strings. So I am a bit flummoxed, but I continue to try to get it dialed in.

As I mentioned, countless dozens of prints are working well. It is this 120x120 one that is so problematic.

Also as I mentioned, moving the speed up from 25 to 50ish seems to have remarkably reduced the problem...which seems counter-intuitive to me.

I am using Prusament. Only.

Sometimes, too many dials being turned at once make things unclear.

I have a number of models that print reliably, perfectly. I have printed many dozens of them without ever a problem. Then, there is this model with a large 120x120 foot and I have consistently had problems with Layer 1.

This right here.........If you have isolated your problem, then you know where to look!  If only a large layer 1 causes an issue, have you tried 7x7 bed leveling in addition to setting your LiveZ?  Take it one step at a time.......if everything works but one thing, don't go off and make changes that affect everything!!

Maybe octoprint/pronterface to help level if LiveZ doesn't do the trick?

As far as stringing and Prusament, here is a print that was running as I have been typing.  It was done using 100% default settings in slicer2.2, with a freshly built MK3S and Carmine Red PETG

Since Prusaslicer 2.2 is now out, I deleted everything I had set up and did a nice fresh install. I'll start with defaults and see how they go.

Sometimes, too many dials being turned at once make things unclear.

I have a number of models that print reliably, perfectly. I have printed many dozens of them without ever a problem. Then, there is this model with a large 120x120 foot and I have consistently had problems with Layer 1.

Now, it is time for the fresh install, fresh start, and learning PrusaSlicer 2.2's changes.

My 1st build produced "ok" parts with the occasional bump or blob damage.....but I found it was 100% my fault with LiveZ and bearings. 

I honestly feel that this entire thing has been made far too complicated.  If the machine can't do the basics with default settings......then there is a physical problem.  Whether age, wear, failure, or assembly......trying to use complicated solutions will only make the basic problem worse.

I am still quite new to this, and so the shared knowledge of PETG liking to creep to wherever it is hottest is insightful. It also does explain why the print sheet is hotter, etc. Thanks for sharing this.

If you really want help, then download this: https://www.prusaprinters.org/prints/13998-bridging-overhang-curling-retraction-thin-walls-to

Print it with your current settings, post your settings on here, no actually post an export from slicer of the actual print so we can verify what you have printed /posted, then listen to what people with some experience have to say.

Were not experts, but colleagues albeit in a hobby (Some in a business), whom strive to help each other in a friendly and helpful manner, then  apply the said suggestions.

Re-print the above with your now suggested settings with pictures of the results and maybe we can work together to get you the results you strive.