I’d make some comments in your processes,
please apply ESD after Back-Geocoding, also I think there is no reason to apply Speckle- Filtering, multillook step could be good solution also to exclude the speckles from the infgm,
If it’s run so for so good, if not, Please remove the subset from the graph, and re-apply the gpt again.
Please take a look a the following post of Create Single Interferogram