Two possible bugs in ArcGIS Runtime 100.10 for feature layer.
1. Label does not rotate when Angle is non-zero.
2. The following SimpleLineSymbolStyle are not saved in Json. When a symbol using them is saved to json and read back, all reset to "Solid".
Long dash
Long dash dot
Short dash
Short dash dot
Short dash dot dot
Short dot
Attach is a simple test project.
We have the same issue.
You could try
Layer.LabelsEnabled = false;
Layer.LabelsEnabled = true;
but that's a bad workaround