Coregistration issue with the slave image

This issue is discussed quite a lot , firstly be sure of your SNAP is uptodate , second thing you mentioned ,

Did you also tried up, SRTM 1sec?

In this case, please take a look at this post, explains, how to select the correspondent slice and frame,

Source of the post

Please take a look at the processing steps in the following post, I explained in details,

Source of the post