Error when uploading files to an SMB server

Hello everyone,

I'm having troubles uploading files on my smb server using files app on iPhone.

To give some context, I use my box internal VPN to connect from the outside of my LAN to get access to an internal smb server. The VPN is working, I can connect to the smb server, view my files, delete files, however I cannot upload anything, it always results in the same error : "The operation couldn't have succeeded. Non found attribute". I don't understand because it works fine on my Mac, and with third party applications.

Is this a bug or I may have configured something badly ?

I thank you in advance for your answers.