When using the ArcGIS Runtime with .NET we are noticing that if we resize an application containing a map, items attached to it do not stay anchored properly and move with it. Upon moving the map in any way, however, the items then snap back into place.
Further notes can be found in the readme documentation at this github repository. GitHub - patdaburu/ArcGISRuntime-DotNet-Maptips-1: A simple demonstration of the use of "maptips" wi...
Note that you can use esri:MapView.ViewOverlayAnchor to bind the location of the overlay as shown here https://community.esri.com/thread/190047-popups-in-arcgis-runtime-sdk-for-net#comment-666876
Not sure if that makes any difference since haven't tested this exact case.