All incomplete work items of a process instance are not migrated.
When a business process is migrated to a newer version, the worksteps assigned to human performers are reactivated and work items are created again based on the performer of the new process template.
For example, consider a process instance with an active human workstep of type ALL with 10 work items created and seven work items already completed before the migration. When this instance is migrated to a newer version, the migration tool ignores all the previously created and completed work items and creates 10 work items again, assuming that the workstep performer remains the same.
All incomplete work items of a process instance are not migrated.