The switch is the pre-wired module anti vandal. It has the quick disconnect jst connector on it for the wiring harness of the nano biscotte V3. I think it would be pretty hard to wire it to the board with the wiring harness directly attached. Im wondering if its not the switch being prewired incorrectly.
The prewired Anti-vandal switch from TCSS has one lead(s) that goes to the switch (yellow) and the other (with the Dynaohm resistor) needs to be wired to the board with a female JST connector. Sounds like you are attaching the male JST to the FOC connector from the wiring harness. (Although, the FOC lead is male I believe, so not sure about this)
Soldering with the wiring harness on is a piece of cake. Just follow the points shown on the NB Manual. I've done it on dozens of builds.
Note the following from the TCSS description of the prewired AV switch:
"For the MWS Nano Biscotti the switch will plug into the switch port but the LED currently does not have a matching connector."
Thus, You need to create this connection with a Female JST connector, usually via the 3.3v and - power pads.