Left button not working on Xbox controller after being replaced

I have a 1537 controller that had intermittent problems with the left button, on metering the switch for continuity it needed replacing.

I replaced the switch and checked continuity again, all is good. However, when testing the controller on the Xbox the switch isn't responding.

Shorting out the switch contacts on the reverse of the board makes no difference. So I'm now stumped as to what this problem could be.

Any recommendations as to what to try next?