Readings did not send to output

Q1:  I have been using your Multiplexer Shield and now it has stopped working properly. It only takes readings from the last thermocouple and outputs that information for each of the 8 inputs.

A1:  My first thought is to check the connections from the host Arduino pins D4, D5, and D6 to the multiplexer address lines. These signals select which input the shield is measuring. They can be affected by bad soldering, interference from another shield, or interference in the code.

The shield is non-isolated and the thermocouples cannot be electrically connected to each other or a common voltage. Some thermocouples connect through the metalwork of their packaging. (Or have no packaging at all and are just the exposed thermocouple bead) If this makes a circuit back to the Arduino power or another sensor, that will confuse the reading.