When the licensing portal in ArcGIS Pro is set to https://www.arcgis.com, is licensed in Organization A, and the active portal is set to Organization B, spatiotemporal feature layers loaded from the Catalog pane fail to load with the error "Failed to add data."
When licensing ArcGIS Pro as a named user through an ArcGIS Online organization, set it to the full ArcGIS Online organization URL, e.g., https://organization.maps.arcgis.com.
Copy the spatiotemporal feature service's REST URL with the token included and add it to ArcGIS Pro. Click Map > Add Data > Data from Path.