If the import stalls and fails to respond after a few minutes You are suffering from PHP configuration limits that are set too low to complete the process. You should contact your hosting provider and ask them to increase those limits to a minimum as follows:
- max_execution_time 600
- memory_limit 128M
- post_max_size 32M
- upload_max_filesize 32M
You can verify your PHP configuration limits by installing a simple plugin found here: https://wordpress.org/plugins/debug-info/. And you can also check your PHP error logs to see the exact error being returned.