First, verify that the toggle switch and the stomp switch are working correctly. Connect the Tensor to our web editor (requires Chrome) or a MIDI monitor application. A DAW will work too, if you can inspect the MIDI data sent by the Tensor.
In the web editor, when you move the hold M/L toggle switch, the onscreen control should also update:
In a MIDI monitor application, you should see MIDI CC #85 with values of 0 (momentary) and 127 (latching).
Next, if you use the editor to set the Hold Switch to Momentary, does the switch work as expected? You can use the left LED to check, without unplugging the Tensor.
If you are using a MIDI monitor application, the Hold footswitch should send MIDI CC #80 with values 127 when pressed and 0 when released, regardless of whether it is set to momentary or latching.