How are tasks sorted?
Tasks are sorted by start date, then alphabetically, and then by end date.
If a phases template is applied, tasks are sequenced by phase (according to the phase order) and then sorted within each phase by start date, then alphabetically, and then by end date.
When tasks have no start date or share the same start date, the workaround to define the display order is to manually number the tasks from 0 to 9 or from A to Z.