I grabbed some screenshots of the errors:
Below is the error I get when launching the survey from the web map popup that I use in Field Maps. This is described in item # 2 above. This was actually generated on the desktop from Map Viewer Classic, but I get the same error when launching it from Field Maps.
If I simply launch the Survey123 web app from my AGOL home page, shown here:
Then close the survey123 web app, I can successfully launch the survey from the web map popup and access the survey with no problems, shown here:
Notice the Icon and my name in the upper right of the screenshot above. After I've launched the Survey123 web app from the browser it recognizes me as being logged in and allows me to access the survey.
I generated these errors from the desktop, but again, I'm getting the same problem from a mobile device.