Acronis Cyber Protect: Attempt to remove backup or recover files fails with "The machine is offline or is not available"

Symptoms

You try to recover or delete a backup via the Cyber Protection console.

The operation fails with:

The machine with ID '...' is offline or is not available"

The machine with Agent is offline or deleted.

If possible, bring the agent back online to perform the operation.

If the original Agent is no longer available, use one of the following solutions:

select another agent in the field Machine to browse from:
or perform the operation from Web Restore console: if you know your data center name (ex. EU2, US2, etc) simply go to <DC>-cloud.acronis.com/wr, where <DC> is the code of your data center. Log in as the original user that created the backups.
- to recover files: browse to the required files/folders, select the data that you want to recover, and click Download in the menu on the right
- to delete the backup: see Deleting backups via Web restore console

If the selected Agent is really online but the error still appears, contact Acronis Support for investigation.