these come from the range doppler terrain correction where the plain image is draped over a DEM. The fact that your image is tilted indicates that it was geocoded to a map projection.
Data to be processed in StaMPS should not be map projected.
https://media.asf.alaska.edu/uploads/Data%20Recipes/GAMMA_before_after_900.png
source: How to Radiometrically Terrain-Correct (RTC) Sentinel-1 Data Using GAMMA Software | Alaska Satellite Facility