"550 Could not get file size" for particular folders

[eku]

I'm trying to backup the SD card in my switch via ftp. For this, as for other consoles, I use wget with the following command line

wget --mirror -c --no-host-directories --cut-dirs 0 --no-netrc --no-proxy --unlink --no-proxy --timeout=1 -P ftp://<IP of switch>:5000/ <local directory>

Some directories produce an FTP error, although I can very well access them via MTP. The consistency of the SD card was also checked.

220 Hello!
USER anonymous
230 OK
SYST
215 UNIX Type: L8
PWD
257 "/"
TYPE I
200 OK
CWD /atmosphere
200 OK
SIZE automatic_backups
550 Could not get file size.
PASV
227 Entering Passive Mode (192,168,55,89,50,60)
RETR automatic_backups
450 failed to open file

mtheall/ftpd has the very same issue.

Let me know, if you need a wireshark log or want me to test anything.

[eku]

Is there anything I can do to speed up error analysis and rectification? Diagnostic data? Should I test something?