Hi ContainingLordP
Sorry to hear you are having issues. Just recently my two stopped working but I had had some issues with some other devices also. I rebooted my router and my other devices started working properly again, but neither of my Invokes picked back up. I unplugged them from power waited a few seconds and then plugged them back up. Before too long they both started working again.
If you have not, maybe try rebooting your router just to see if it would help? I don't think MS has done any updates at least that have completely left my two not working.
I do know how frustrating it is though. MS did a lousy job pushing Cortana. She could have been the go to assistant had MS had stayed at it. She was better than Siri in the beginning. (and still is in some ways in my opinion). Alexa and Google had barely started. Like many things with MS. An opportunity lost.
Good luck.