The issue was reproducible with a User with view permission and a User with Site Content Reviewer role.
- Add a new Site "My Site"
- Add a new User
- Add User to "My Site"
- Assign roles: Site Administration and Site Content Reviewer
- Save User
- Log in as new User
- Go to "My Site"
- In "My Site" go to Configuration > Workflow Configuration
- Set Single Approver for Calendar
- Add a Calendar portlet to a page
- Add an event > Submit for Publication
- Go to My Account > Notifications
- Click on Calendar notification message
User is navigated to My Workflow Tasks portlet to view workflow submission.
The User cannot access My Workflow Tasks portlet. If you navigate back to My Account > My Workflow Tasks > Assigned to Me, you are able to access My Workflow Tasks portlet and assign/approve workflow submission.