Firstly, find out if it is a Hydration problem.
Switch Hydration off, rebuild and install, then launch the app. Does it still only display and empty screen?
BTW: be aware that config changes are ignored as long as Hydration is enabled while building.
Wow...well that worked immediately, thank you!
Is there a known issue with enabling hydration?
Thanks for your help.
Not sure about a 'known issue', because I don't use Hydration. That facility adds a wrapper-index.html, which in turn launches your own index.html. The Hydration-index has its own settings and config/whitelisting, which is not exactly what you set for your app. For that reason, Hydration doesn't really reflect the future production environment of your app and in that sense it's of limited value when it comes to serious testing processes.
Due to this mechanism, the config of Hydrated apps can't be changed. If you want to make config changes, you must disable Hydration, first. I find it a pain in the butt.
Perhaps, in your case, Hydration got stuck with (partly) changed configs or perhaps a new CSP in your app. I'm not 100% sure, though.