Issue: When you assign a particular person to this workitem, Issues like this might occur.
This error occurs due to the fact, that the user who have put in Assigned To is not identifable by Azure DevOps . This might be due to the fact that either the user is not in the organization or the user has not been added to the organization.
- User might not be in the organization (or) you are trying to add a person from outside the organization
- User has not been added to the Azure DevOps