Backup - Unexpected end of archive

Hello,

It’s been around 2 to 3 months that I have an issue with all my backups.

I’m sending backups through sftp and everytime they seem to be uncomplete.

I always have “unexpected end of archive” and when I open it there is like 4 out of my 15 websites and they are not complete.

What could I do to know what is happening here?

Thanks in advance