The End Date of Project tasks are not updating to the new value and revert to a different value. The value is set on the form but not saved on the record.
The new date is set from the client script "Check valid task start date and set end" which is calling the script include AjaxProectTaskUtil. This happens to a specific project, it works correctly on other new projects.
There are many stale task records under the project, i.e., the top task is a project but its parent is empty, resulting in this scenario.
We usually keep track of the hierarchy of tasks with two fields; Top Task and Parent. The affected project has over 140 task records that have a Top Task field but with the Parent field empty, leading to this issue.