The cause is in the deployment template that has some options set which do not fit multiple machines deployment. As a result, some of the machines are left out

It is recommended to use administrator credentials (user is better to have at least Backup Operators or Administrators membership) when you create a backup plan.

When you create a backup plan, the product by default sets the access credentials of the user under which you are currently logged in on the current machine or connect to a remote machine with Acronis Agent.

To set the credentials explicitly, you will need to click Show plan's credentials under Plan parameters: