(s)ftp issues on nano so sw6.4

[FraSti]

Facing an consistent issue always present even after updating, downgrading another update and factory reset:

the proxy-sftp task is taking lastexport.txt an uploads the file with following failures:
a) the file is not deleted and the export folder started accumulating files (option delete is set)
b) the placeholders in the filename are not replaced => day-[YYYY]_[MM]_[DD].csv the format of the export file was ok

I am wondering, if a system file could be corrupted, because latest software and reset has not resolved the issue.

Any advice

Thanks,
Frank