As you’ve correctly identified, there is a UI limitation where the switch UI widget will not work properly with Items with NULL or UNDEF states. Such are assumed to be ‘off’ so no OFF command can be sent.
You might confirm that is your issue by examining your Item state - there are are other possible causes for the same symptom.
That’s your real problem, which it would be desirable to fix. I don’t know anything about LightwaveRF.
However, openHAB includes a feature ‘autoupdate’ which essentially guesses the likely outcome of commands and updates Item state accordingly.
In your case, the ‘broken’ Alexa feedback is probably suppressing this action.
See “binding veto” here -
You may be able to circumvent this by forcing autoupdate mode.
But that won’t help if Alexa is positively setting UNDEF state. Check in your events.log what is going on with your Item, by way of commands, predictions, and state changes.
