Are you importing a large volume of contacts? If so, best practice is to leave the site for at least 30 minutes to ensure the contacts can be imported without issue.

If you leave the site open, you may see a page unresponsive message.

This is normal and does not mean the import has stopped, it’s still running in the background.

Because of the potential unresponsiveness during the import, it’s best to do these out of operational hours to decrease the risk of interrupting other user's activity during the day.