We are seeing lots of RFIs in Denmark.Looking at a 2 year time series they change size and position. Sometimes they are very faint, what is very tricky.
Btw. there is a Google Earth kmz which shows location of ground based radars at SAM sites (not up to date, of course) which may interfere with Sentinel-1 C band. https://www.gearthblog.com/wp-content/uploads/2016/04/SAM-sites.kmz
These authors have also taken a look at them and are still working on a solution on detecting them.