Geometric correction drags zero pixels from DEM to the S1 corrected

Im trying to correct a S1 (GRD) with an external DEM (Alaska facility, ALOS 12.5 m hi res), pre process chain is: apply orbit file - remove GRD border noise - remove thermal noise - calibration - speckle filter (single product IDAN) and Terrain correction Range doppler. Values in terrain correction tool are: external dem, non checked earth gravitational model, DEM and image resam with bilinear interpolation, 10.0 m -10.0 m, and pixel spacing same, GRS 32616 and just checked selected bad source.

The thing is the image result comes with black pixels that looks they are zero values in the original DEM (This DEM has values from -52 to 252, but this is a coastal area, sounds weird -52 values).
I’ve tried to reclass zero pixels, and result is the same, I´ve converted negative values to zero and it went wrong cause it disappear most of the image.

Any thoughts? Thanks in advance.