I think the problem was caused by that the product crosses the 180th meridian. Because of that, part of the geocoding of the product is incorrect which leads to the artifacts in the Terrain Corrected image.
This is a known issue and has not been fixed. Post of similar problem can be found at Terrain corrected S1 data crossing the antimeridian are shifted into the Western Hemisphere. The issue has been tracked by ticket https://senbox.atlassian.net/browse/SITBX-647.
If you can create a subset of the image and make sure it does not cross the 180th meridian, then the processing result should be fine