Overwriting a layer in Portal for ArcGIS converts the existing symbol markers to images, leading to quality degradation with each subsequent overwrite.

Workaround

Option 1: Reconfigure the symbology after each overwrite.

Option 2:

1. Publish a hosted feature service.
2. Use Add item > From a URL and create another layer item using the original service URL. 
3. Apply symbology on this new layer item that was just created through the Visualization tab. This preserves the symbology to only the layer item and can be shared and used in maps and apps.

Steps to Reproduce