Wondering if this is a bug. Noticed it today on my site but I am seeing the same issue on any publicly-accessible arcgis online site (anonymous access allowed with publicly-shared layers).
Visit an arcgis online site, click on Map>Modify Map and Add>Search for Layers. In the past, you would get a list of all the publicly-shared layers for the organization. Now, it just hangs on Loading Items... and doesn't populate the list.
The layers are available as I can search and add them to the map from the one million layers in the generic ArcGIS Online option, just not from the Organization.
I tried this in Chrome and Edge with the same results. Tried multiple arcgis online sites with the same results.