I’ve done some more testing on this. The issue persists, but there is a workaround.
The issue is specific to the allowed values/dropdown menu observation fields. No edits to these fields are saved in the app. Edits to simple text-entry fields w/o allowed values save without a problem. Adding an existing observation to the project for the first time and completing observation fields also seems to work fine.
The only way I have found that I can change existing values for dropdown observation fields is to remove and re-add an observation to the project. This resets all observation field values, so I have to start from scratch, but the values I enter when I do this are saved. I can tell when an observation saves because I will see the green upload bar when I exit the observation.
No green upload bar is shown when I simply try to edit the field values.