Christian, did you ever resolve your issue? I've seen some various SFTP issues posted on this forum about potential mismatched ciphers but don't seem to find any outcomes/solutions. I have a couple clients with newer SFTP server software where I get upload disconnects with larger files. I have no issues with third-party FTP clients, and even matching the ciphers used by Automate with the standalone FTP clients doesn't seem to help.
If you do %WeekdayName(Weekday(Now))%, it returns Tuesday for today. You should be able to see more information in the BASIC scripting part of Automate's help file.