It's not certain why this occurs (during the normal DB-indexed based processing the temp files are always produced, but when directly processing SAFE.zip files sometimes GAMMA doesn't produce those files even though there's no processing error) - it probably should be investigated while fixing the error (just need to check files exist before deleting them)
There exists a bug in the S1 processing where it will try to delete temporary files that do not exist, located here: https://github.com/GeoscienceAustralia/gamma_insar/blob/pygamma_workflow/insar/process_s1_slc.py#L769-L770
It's not certain why this occurs (during the normal DB-indexed based processing the temp files are always produced, but when directly processing SAFE.zip files sometimes GAMMA doesn't produce those files even though there's no processing error) - it probably should be investigated while fixing the error (just need to check files exist before deleting them)