Open Thermocouple when heated

Hello, new to the site and first time poster.

I have a grounded dual element T/C that measures the bearing temperature on a reciprocating compressor. When the machine is down, the T/C reads fine at about 40 deg C. As soon as the machine starts, the T/C PV goes high indicating an open T/C. Has anyone had this happen before?

Is it possible the T/C could have a small break and when it is heated, it expands and breaks the loop? The other element is currently reading 60 Deg C with the machine running.

Could also be vibration, but if it's consistent rather than intermittent, you're probably right about the temperature.

I had a gas valve like that on a burner once. Fires right up, runs fine for about 10 minutes till the valve warms up and the broken wire in the coil opens.