So I have run into the same issue today and figured out another "fix" for it.
I am using ArcGIS Enterprise Portal 10.9.1 and ArcGIS Field Maps in a disconnected environment (no internet). I was attempting to make a map area in Field Maps for use on a tablet and encountered the above issues. I set all the sharing permissions for everything (web map, feature layers, and service definitions) to be the same and tried again: no dice.
I ran some smaller tests (I was originally trying to make a large map area) and found that a small test in one area worked while another of equal size did not. The difference between the two? The one that did not work contained features that I had collected previously using Field Maps mobile.
I got rid of the error by deleting all the features I made (they were only test features) and then retrying the large area. It worked.
This is obviously not ideal so... @Esri get on it please and thank you.