Tracked down the root cause.
One of the Thermocouples was in a water bath and the shielding on the end of the thermocouple exposed the tip to the water bath. This was allowing transients to interfere with the TC-08. After shielding the tip, problem went away.

I am running 3 TC-08 USB loggers on a Windows 10 64 bit environment. The data on 1 of the TC-08 units started to show instability and drift higher in reported readings. The data on another unit on one of the channels was reporting about 5 to 10C lower than actual. I verified that the data was inaccu...