I found with the newest update (Fall 2025) that the issue of swipe with a basemap was still acting wonky for some of my students who had georeferenced an image but were using the imagery basemap. What we found as a solution when there is only 1 layer (historic image) and a basemap in the Media (Basic) instant app or other apps. Once it recognized the webmap then the hack was that we did NOT select a leading layer. We only selected the historic georeferenced image in the trailing layer and it worked. I don't know why it worked, but I think it's because it's expecting 2 layers in that webmap that it's pulling from instead of one.
And one thing I found students also found confusing was the Swipe App vs having the swipe tool embedded in the Basic App or the Imagery app. If I could wave a magic wand I would rename the Swipe App that is more focused on timeline based data (so Time Swipe or Time based App?)
For more detail and context of one of my student's who had this problem. She worked through this lesson: https://learn.arcgis.com/en/projects/georeference-imagery-in-arcgis-pro/ from the Esri #LearnLessons
Uploaded her final product of the State College of PA data through ArcGIS Pro as a WebMap.
Because the historic image is the only output in that lesson that she wanted to upload and share in her storymap portfolio (and later a possible website that she could embed the map) she chose to not just add the map in the storymap and create the swipe there. She wanted the flexibility of the webapps. From the instant app options she tried Basic and she had tried the Swipe App. I had her try imagery app. We returned to her first Basic Media map and used the solution I wrote above to make it work.
