I can see an old sample/training process with Process Owner and Process Expert - Promapp Promaster. However, this user doesn’t seem to exist in our user/role list.
Please advise where is the Promapp Promaster role appearing? Please refer to the screen shot attached.
I'm not sure whether you attached a screenshot as I can't see one attached to your post.
If a role doesn't exist in your system your Promaster can add it for you. Other staff may be able to add it also depending on your configuration settings.