I recently upgraded our ArcGIS Enterprise installation from 10.6.0 to 10.6.1. After the upgrade, we found that in the browser based applications (e.g. the Portal Map Viewer, Web App Builder applications) the geometry for selected features for some of our key GIS layers get rendered incorrectly at larger map scales. The source of the features are Map Services provided by ArcGIS Server. The drawing or rendering issue appears at around AGOL map scales of 1:2,257 and larger. Polygons get rendered incorrectly as jagged lines and it appears that many of the vertices are dropped from the rendered polygon. Some vertices for selected linear features also appear to be dropped causing the selected linear feature to be drawn with an offset. This rendering and drawing issue with 10.6.1 does not effect our layers with simpler geometry but does seem to effect layers with a very large number of vertices present in the underlying polygon or linear features.
The first attachment provides an example of the rendering/drawing problem with a selected feature. The second attachment show the large number of vertices present for the shapes in the source polygon feature class.
This rendering/drawing issue did not occur with previous versions of ArcGIS Enterprise 10.5.1 and 10.6.0 that we have used and does not occur with the Map Viewer and Web AppBuilder applications used with ArcGIS Online.