Sadly, the speed of this process is directly related to the web server capacity and there is nothing we can do to speed things up.
This can be achieved by increasing RAM, CPU, mySQL resources, etc. You can ask for it to your hosting provider.
But, to make sure this was not stopped suddenly on the server side when it was importing due to an error, I would recommend checking your PHP error log.
If you need to know how to enable and/or get this log, please read this article:
If you see any errors related to ATUM there, you can open a private ticket and attach the file there, so we can take a look.