In ArcGIS Enterprise Map Viewer, when switching the layer search from the default 'In: ArcGIS Enterprise' to 'In: My Content' with 'Within map area' unchecked, not all results are displayed.
This issue is no longer reproducible in ArcGIS Enterprise 10.8.1, which is the current minimum supported version of ArcGIS Enterprise. If issue persists in the newer versions of ArcGIS Enterprise, contact Esri Technical Support with the steps to reproduce.