Reading through the datasheet some more, I realized that we weren't checking the CRC for the scratchpad register. This was causing some invalid readings to get through sometimes. You can see this when you plug a probe in it will occasionally flash to 999 for a second, then start showing valid readings. Another user has seen this happen when switching on certain loads with the Model-T. This condition is detectable as an invalid scratchpad CRC, so I just added some checks for that.
@bmoney also added some filtering of the readings to smooth them out a bit on the plots and make sure that huge jumps in readings are not included.