Print removal with larger metal tool can cause display to blank, flicker back after a few seconds
Having started with a Mk2 and similar non-removable bed printers, I've been in the habit of removing prints (once the bed has cooled) using a broad (6"/150mm) drywall joint knife (I've filed the corners round) and continue to do so when bending the sheet doesn't work (small ASA parts stick too well). Just got a Mk3S+ (kit) and I noticed that when I do this, sometimes the LCD will blank out for a few seconds and eventually flicker back in.
It's not pressure pinching a wire somewhere; it has to be a metal tool of sufficient size (probably beyond what Prusa had in mind by "spatula with rounded corners") and it seems like I have to go pretty much all the way across within about half a second. While doing much the same, I had never observed this screen blanking on my Mk2 (upgraded to 2.5, 2.5S).
I unplugged the printer and removed the heat bed connector cover so I could check it out with an oscilloscope. Sure enough, when I do this, I can measure a spike of at least +/-3V between the heat bed screws, presumably caused by induction when moving the metal across the copper foil "coils" of the print bed. (Looks a little bit like what you get if you forget the clamping diodes around a relay.)
I'm presuming this isn't good for the circuitry, so I will simply be trying to retrain myself not do that as the most expedient solution. But I thought I would share this information / experience in case anyone has additional thoughts or is experiencing the same without recognizing the (hopefully small) potential to damage the board.
Interesting troubleshooting
I'm genuinely impressed at how you did the troubleshooting here.
It's never really occurred to me to leave the steel sheet on the magnetic bed when removing a print, it just seems safer to avoid applying force to the heated bed.