When attempting to open a form using the 'Open in Survey123 for ArcGIS' button on the item details page in ArcGIS Online, Survey123 for ArcGIS launches but returns the following error, "Survey not found. Survey id undefined has not been downloaded," and the form does not download automatically as expected.
Download the form manually. To avoid the error, open the desktop application of Survey123 for ArcGIS rather than going through ArcGIS Online.
Through either medium, on the right-hand corner, select the menu (three lines) button > Download Surveys, and search for the form.
Alternatively, create the URL from scratch using the workflow in the following blog post, https://geonet.esri.com/groups/survey123/blog/2016/07/30/understanding-survey123s-custom-url-scheme. Be sure to include '?itemid' as part of the URL.