I have gone through this project and assured all layers and features are marked share public, but the application is still requiring individuals to log in to see everything. This is a problem because it was created for individuals who are not ArcGIS account holders.
Here is the app link: https://experience.arcgis.com/experience/841ec133761b445a8e1e33ae9953b753
Please let me know if there is anything I can do to fix this. The map is public, but when in the application, it is not.
I just tried again and this time there was no login prompt, no errors either, and all the layers loaded properly for me this time.
Thankfully I was able to resolve the issue! Apparently using the 'Replace Service URL's' tool in AGO Assistant did an incomplete job. It did not replace all the required URL and itemIds in the JSON file, so it was still secretly referencing the old service, which still had security enabled, even though it appeared to be referencing the new service. I copied the JSON code into a text editor and then used find and replace to find all instances of the outdated itemId and URL and updated them to the new one. Once I did that, it worked like a charm!