We recently recreated a Survey123 survey in Portal for ArcGIS. The survey has 2 "picture" questions and 1 "signature" question.
The survey was previously in AGOL, but I downloaded the feature service including the attachments and loaded these records into the survey feature service hosted in Portal.
The feature service in Portal has the attachments, and the attachments can be seen in the feature service data tab, but the Survey123 form is not "aware" that the attachments go with each of the three survey questions. For instance when viewing the survey in edit mode the three questions show no image, and when generating a Word Doc report the picture attachments are not shown for the questions.
What is the mechanism by which Survey123 relates a question to an attachment file so I can resolve this?