Task is incorrectly marked as a Milestone even though it is not 0 or 1 day duration and even though the task also has assignments for a project that uses Microsoft Project (MSP). The milestone check box is grayed out in Clarity/PPM, so you are unable to change the task back from a milestone to a task.
To change the milestone back to a regular task
1. Export the project to MSP
2. Double click on the task with the issue
3. Go to the Advanced tab
4. Uncheck the milestone check box
5. Save the project back to PPM