Problem while using Coregistration

Hello everyone,
I am discovering SNAP and doing a few small personal projects to learn the programme as well as possible.

After following the tutorial on change detection, I’m trying to apply the same concepts to different products.

During the Coregistration step, I get a stack with my two VV amplitudes images, but only one of them is visible:

Do you have any idea what might be causing this problem or how to solve it ?

It seems that the first image has been terrain corrected. I think you should use the SAR domain images for the coregistration.