Terrain Flattening ALOS2

I have a weird issue when I try a terrain flattening workflow in the Netherlands area.
The data is an ALOS2 1.1 quad-pol data, and the workflow is as follow:

  1. Radiometric calibrate → create beta0 virtual band
    2)Radiometric Terrain Flattening
    3)Geometric Terrain Correction → Range Doppler Terrain correction

The result I get looks like data along what appears to be diagonal lines and no data in between (see image)