So, following:
cd \path\to\reactor
node tools\install_reactor_windows_service.js -u .
del /s /f node_modules
npm rm -g node-windows
npm uninstall node-windows
npm uninstall -g node-windows
npm install -g node-windows@1.0.0-beta.6
npm link node-windows
...extract the Reactor.zip over the old directory...
node tools\install_reactor_windows_service.js -i .
I'm now running fine with Reactor (Multi-hub) stable-22136.
Thank you @toggledbits for your support and amazing product.
Bonus is the SSL now works too (CertifytheWeb with LetsEncrypt will renew it and drop the key files in the correct location). That means I can have Reactor as a tab in the Hass sidebar (previously https Hass --> http reactor would not work).