ScottG:
What exactly did you change in the code? I have three thermocouples connected to three Adafruit breakout boards. One is connected to a motor housing. The other to are in thermowells measuring water temp. I have had lots of problems (mostly reading 32F) maybe this grounding issue is the cause.
I commented out Adafruit_MAX31855.cpp, line 71-74:
// if (v & 0x7) {
// // uh oh, a serious problem!
// return NAN;
// }
The MAX31855 will return the type of error that would get you the 32F reading. Use Adafruit_MAX31855::readError(). I don't have the error codes here, but it will tell you whether the probe is open or grounded.
Holger