puck lite problems

Thanks for doing that test - and that was with everything disconnected? so no resistors or anything on it? That would definitely seem to imply some kind of hardware failure if so.

they frequently have low to very low impedance between pins 30 and 31

Looks like the self-test backs this up too. Interestingly though it looks like D30/D31 may have ended up partially connected together as it seems like if D31 is floating, D30 can still read a value?

I just wanted to check - there's nothing like water damage that might have happened to the Puck? Salt water/sweat between the pins could explain something like this too.

What's the circuit?

• Sensor attached between D30 and D31
  
• Resistor from D28 to D30?
  
  

If you could switch to putting one since of the sensor directly on GND, I think that could help a great deal. As-is, any static electricity that makes its way along the wire is going to go right into the IO pins - and that could be causing the problems you're seeing I guess.