Issue with subset+snaphu export after Tops merge

My aim is to merge three swath , subset the study region before unwrapping and then proceed to unwrap.

For each swath, I followed the process as follow

Topsar split>Back GeoCoding> Interferogram Formations ( Multi Reference InSAR )

In next step, use the output of each swath ( IW1+IW2+IW3 ) to create merged product using Tops merge

Now if I only use

merge_output > snaphu export

or if I use merge_output > subset> write

This don’t raise any error and process successfully, But if i try to subset and use snaphu export of merged output, then it raises multiple errors such as operator exception error and sometime wrapped phase required error and also stacked product is required error.

is subsetting of merge product and exporting for snaphu unwrapping is not possible? Do I only have option to snaphu export using whole image?

In case, if my study area is between multiple swaths, should i snaphu export , unwrapped them and import them and then merge them? is this correct process workflow?

Summary

Tops merge>snaphu export (works)

Tosp merge > subset > write (works)

Tops merge > subset > snaphu export (throws error)