I have the same issue. When I run the backup, everything works fine until completion, but when I switch to the overview it shows only 65% and the size is zero KB. But when I check the files in wp-snapshot, everything is correct there, also the log file tells not a single error.
The weird fact is, I have this issue on the same server with equal settings on some WordPress instances and on some not. There is also no difference in the used plugins and their configuration (except the domain and path, but even the folder permissions are equal). I guess there is a problem with file checking the files at the overview.
The problem is that I cannot create a new backup until I remove the 65% entry. I am completely frustrated because I get nowhere a single error (also not in the PHP-logs or in the Apache logs).