Dear ABraun, thanks for your reply.
“Remove antenna pattern” should be valid on ERS/ENV data but not for S1, see also here:
I tried Thermal noise removal but it returned an empty product (note we are using S1 SLC not GRD and also need to maintain phase information)
Calibration was already applied as mentioned in the first post.
The issue seems to be generated in one of the BackGeocoding or “Enhanced spectral diversity” steps.