Summary task dates in PPM do not reflect the dates of the child tasks underneath it.
For example, the start date of the summary task may be years before the earliest date of any of the the child tasks.
It has not been determined how this issue occurs.
In the PPM gantt, outdent the child tasks under the lowest summary task that is affected and indent those same subtaks again. This will trigger the date on the summary task(s) to update to the correct dates reflecting the dates of the child tasks.