Why this alert is displayed:
The software checks the progress of the backup task and other activities every hour. This alert is displayed anytime the software detects there has been no progress of any kind (bytes sent, disk activity etc.) for the past hour.

When the alert is deactivated:
This alert is deactivated once we detect the backup/activity resumed or completed.

How to troubleshoot this issue:
The issue might be caused by a lockup. Follow this article to collect necessary troubleshooting information. Contact Acronis Support for assistance.