I recently was trying to terrain correct a Sentinel-1 image. The image covers land and water.
The problem seems to be that when SNAP searches for a DEM it expects one must exist. The image I am using (S1A_IW_GRDH_1SDV_20201104T224257_20201104T224326_035105_0418C7_545E) has the north east corner that puts part of the image in the N12W068.SRTMGL1.hgt.zip tile. However, the N12W068.SRTMGL1.hgt.zip does not exist since it is all water. However, the s/w repeatedly looks for the DEM and tries to unzip it:
so SNAP wants to access a SRTM tile which does not exist.
You could create a raster (constant 0) in the same format and spatial resolution and place it inside the aux folder so SNAP takes this instead.
Yes, it seemed that there were two different topics being discussed. So it was good you separated the two threads.
But I thought I would let you know that the DEM download in SNAP produces an empty zip file for non-existent tiles. So, that is why the error shows up as a zipfile problem which obscures the fact that no tile exists. Not sure if that is the intended behavior.