Sentinel -1 data processing

I’m processing an old dataset from Sentinel - 1 (2016) with SNAP and I’m following all the steps required to perform interferometry and obtain informations on the elevation. While the processing has been performed successfully, the result has a very low quality and the coherence results low, even if the two datasets are coherent with each other.
I would like to know if someone else has my same problem with old datasets
Thanks in advance to who will help me