Hi there, thanks for the additional information and a copy of your survey.
I used your xlsx file and published a new survey and created a feature service based of it, and tested using the field app to create new records in the feature layer and also edit records via Inbox in the app to the same existing records in feature layer. I do not see any data loss or null values for fields that I edit via the Inbox and submit. All values entered or edited in the app and visible in AGO in the feature layer.
The only difference is that you are using existing feature service with existing data not created in Survey123, whereas I created the feature layer via Survey123, and all the records via the app.
The only other thing I can think is that it has something to do with your relevant statement on the groups. If the user makes the group not relevant, all questions inside that group also become not relevant. This will make all the values null. Is it possible they are changing the relevant condition that then effects all the related questions, clearing the previously stored values?
Are you able to provide example of exactly what fields had null values even though values were submitted?
On a side note, while reviewing your xlsx file, I noticed a few issues:
1. You have html formatting tags that do not have closing tags. See Survey123 documentation on supported HTML formatting: Quick reference—Survey123 for ArcGIS | ArcGIS
2 You are using named notes, which in turn creates a field in the database just for the note, so will never have any values as is not an input. You can either remove the name in the name column of a note, or add a esri field type of null, so that a field is not required in feature layer that is never used. Notes—Survey123 for ArcGIS | ArcGIS
Phil.
