I have tried manually polling via "Poll Now" under commands, but this times out.
This is a communications issue. Something is impeding the signal(range, obstruction, interference), or there is a bad route. The latter could be fixed by excluding(resetting) the device and including it anew.
My system isn't very big at all, 6 devices so far
An elevated risk of weak signal and poor mesh.
all well within range of controller.
Unless the switch is 1 or 2 meters away from the controller, I would not make such a blanket statement. There are many possible reasons that the signal could be unable to reach what you assume to be the device's range.
I would suggest that you locate Vera and the switch 1 or 2 meters apart, exclude and include the switch, and then see if polling works. We can safely assume that Vera is good since other switches work with Vera. So, if this switch doesn't work at this short distance, then your switch is likely bad. If it does work at short range, then you've proven that you have a signal issue to overcome. You can do this by, adding devices and improving the mesh, relocating devices to improve signal quality, eliminating obstacles and interference...