After a few days notifications stopped working.
(everything works correctly with the web app -- I have a fixed IP).
I figured why not remove the Android phone device and reinstall it. I did the following:
remove the mobile device in the web app locally
removed and reinstalled the mobile app on Android.
Now the app will not connect with my hub - It says the C-8 hub is unresponsive, but it still gives me the option to select the hub -- which is clearly online from portal.hubitat.com
The app either spins at the stage "Loading Mobile Devices" and peridodically throws an error like "okhttp3ResponseBody$1@22Bf706"
Correct because the arp table had not been flushed so the routing still worked locally and yes it will stop the portal from working. So your fix above was the solution to your problem.