Why is project status change workflow erroring if project team member doesn't have a user account?

Summary:

We are facing issues with Project Status change request workflow when a Project manager or a team member assigned on the project does not have a user account (Employee is created to be used as a PM or team member). Project status change workflow runs into error in such scenarios.

Questions for the Community:
Do you know the reason behind it and any possible workaround other than creating user account of all employees present in Oracle Fusion?

Content (please ensure you mask any confidential information):