Hello all,
in ArcGIS Runtime 10.2.7 .NET, ArcObjects 10.8.1 and ArcGIS Pro 2.8.3 the lines are displayed correctly. In ArcGIS Runtime 100.13 (from MMPK) it looks like this:

For reference (ArcMap from MS SQL-Server):

If we import the mmpk-file into ArcGIS Pro back, it looks "normal" like in the ArcMap display.
Is there something wrong with the display engine in ArcGIS Runtime or is the data to complex?