Thanks again for the thoughts and suggestions, and they have resolved the issue. In case someone else experiences the same issue, here is a summary:
Issue: GX50HW-US. While I can log in on both the web and mobile app (iOS), no data is shown, the firewall says offline, and I get the following message pop ups: "Invalid API Key" & "Network Error" on various screens.
Resolution: Delete and reinstall the iOS app, log in on the iOS app. On the web browser, clear the cookies for "web.meraki-go.com" and "meraki-go.com" Then launch the Meraki Go browser page which will now ask for username and password. Once logged in, all data should display properly.