Are both images form the same orbit Ascending or Descending ?
And Are they cover the same slice and track number?
In step one , did you select the same number of bursts and IW, of each image?
Did you use SRTM 1sec HT, auto download? (This doesn’t cover your study area, should not be selected and SRTM 3sec either)
Is your machine connected to the internet?
IF the answer of the previous questions is , yes , it means your SNAP has problem,
Because you mentioned, that you used other products and the results are same!