Jeff Riley confirmed this issue exists (dropping WiFi connections when switching manually between Wired and Cellular mode) - his email of Feb 13th, 2017:
Thank you for your patience with me while I worked to get caught up again, I have had the opportunity to lab this up and test, my findings are in-line with your observations. As a WiFi LAN client I was dropped when manually switching both ways, from wired to cellular and back again. I then loaded up a more recent firmware version and retested to find the same results.
I have been coordinating in real-time with the engineering team for testing while at home and will contact TK and engineers this evening to determine what our next steps will be. I hope to have some news to report tomorrow. Thanks again for your patience with me Phil, I will pass along news as soon as I have something substantive to report.
Has there been any progress on getting this fixed?