@BJM-Maxx -- I may owe you some thanks and grattitude.
I went back and read thru the entire thread you referenced:
I admit that it took me two or three times reading thru it to finally grasp the technical portion of what was discussed. Its been about 20 years since I had any education on electronics in my college physics classes -- I'm still relearning some of the vocabulary and fundamentals.
My laymans understanding of the situation is when the flipper is grounded/activated an electrical signal is carried along the wire. Perhaps with aging insulation, conductive coil dust on the harness, or just bad luck the flipper signal may occasionally "jump" to the switch matrix harness -- causing issues with the MPU board. The reason for the randomness is due to the wave pattern -- the flipper would need to fire at the end of a strobe pulse (?) to trigger a random pop bumper fire. . . or in my case a reset on the MPU. The referenced thread discussed ways to minimize interference across the wires. Again, my interperetation may not be factually accurate but it is how I make sense of it.
I started with a suggestion from @MrBally to remove the tilt ball from its track. Apparently the metals can oxidize and cause "electrical noise on the switch matrix" (quoting MrBally). My track looked clean but the ball was a bit of an oliveish color vs. shiny metal.
The next suggestion from @BJM-Maxx was to put some distance between the switch matrix wires and solenoid wires on the playfield harness. Looking at a before picture you can see the switch matrix harness (J2 on the MPU) is very close to the flipper wires and other playfield solenoid wires in the backbox.
I snipped some zip ties then re-zip tied the switch matrix harness (arrows) separate from the other wires as far as I could down to the playfield. I put new zip ties back on the main harness as well.
Fired up the game with these two changes and probably played 20 games. . . with ZERO resets.
I do not know if my reset situation has been completely cured but today was very promising. Next I want to do a comparison side by side with the old vs. new CPR backglass. Once it is installed I will move the machine from the shop to the game room at home; I am really enjoying what the game has to offer so far. . . pure pinball at its finest!