In the Outbox if you select the red icon a pop up should appear, does that pop up have any additional error messages?
I would suggest reaching out to Esri Technical Support to further troubleshoot the behavior, a few things that will help in debugging are:
- Please enable diagnostic logging in the Survey123 field app and pass them along for analysis.
- What type of authentication is your ArcGIS Enterprise organization configured with? (IWA, built in, SAML, etc)
- Is this happening only for 1 user or all users submitting this survey?
- What version of Survey123 Connect was the survey published with?
- If using the latest 3.16.105 version of Survey123 Connect please double check that all fields in the XLSForm match the fields in the feature service.
Can you provide some more detail about the layer, like its schema, etc? And can you turn on your browser's developer tools and watch the Network tab when you attempt to send a new form? You may see additional details in the response there.
Are you able to edit the underlying data source in ArcGIS Pro / AGOL?