@Rag3lib Hello!
Sorry for a delay!
Presented below is the code sample which generates the correct file
var t1StartDate = new DateTime(2018, 7, 9, 0, 0, 0);
var t2StartDate = new DateTime(2018, 7, 9, 0, 0, 0);
var t2EndDate = new DateTime(2018, 7, 19, 0, 0, 0);
var t3StartDate = new DateTime(2018, 7, 9, 0, 0, 0);
var t3EndDate = new DateTime(2018, 7, 27, 0, 0, 0);
var project = new Project(Paths.BugsFolder + @"TASKSNET-2686/Modele_Planning_paysage.mpp");
project.Set(Prj.NewTasksAreManual, false);
project.Set(Prj.StartDate, new DateTime(2018, 7, 9, 0, 0, 0));
project.Set(Prj.FinishDate, new DateTime(2018, 8, 31, 0, 0, 0));
var calendar = project.Get(Prj.Calendar);
Task t1 = project.RootTask.Children.Add("Task 01");
t1.Set(Tsk.Calendar, calendar);
t1.Set(Tsk.ConstraintType, ConstraintType.MustStartOn);
t1.Set(Tsk.ConstraintDate, t1StartDate);
t1.Set(Tsk.Duration, project.GetDuration(5, TimeUnitType.Day));
var resourceAssignment1 = project.ResourceAssignments.Add(t1, null);
resourceAssignment1.TimephasedDataFromTaskDuration(calendar);
var t2Duration = (t2EndDate.AddDays(1) - t2StartDate).TotalDays;
var t2 = project.RootTask.Children.Add("Task 02");
t2.Set(Tsk.Calendar, calendar);
t2.Set(Tsk.ConstraintType, ConstraintType.MustStartOn);
t2.Set(Tsk.ConstraintDate, t2StartDate);
t2.Set(Tsk.Duration, project.GetDuration(t2Duration, TimeUnitType.Day));
var resourceAssignment2 = project.ResourceAssignments.Add(t2, null);
resourceAssignment2.TimephasedDataFromTaskDuration(calendar);
resourceAssignment2.SplitTask(new DateTime(2018, 7, 11, 0, 0, 0), new DateTime(2018, 7, 12, 0, 0, 0), calendar);
var t3Duration = (t3EndDate.AddDays(1) - t3StartDate).TotalDays;
var t3 = project.RootTask.Children.Add("Task 03");
t3.Set(Tsk.Calendar, calendar);
t3.Set(Tsk.ConstraintType, ConstraintType.MustStartOn);
t3.Set(Tsk.ConstraintDate, t3StartDate);
t3.Set(Tsk.Duration, project.GetDuration(t3Duration, TimeUnitType.Day));
var resourceAssignment3 = project.ResourceAssignments.Add(t3, null);
resourceAssignment3.TimephasedDataFromTaskDuration(calendar);
resourceAssignment3.SplitTask(new DateTime(2018, 7, 11, 0, 0, 0), new DateTime(2018, 7, 12, 0, 0, 0), calendar);
resourceAssignment3.SplitTask(new DateTime(2018, 7, 24, 0, 0, 0), new DateTime(2018, 7, 25, 0, 0, 0), calendar);
project.Save("result.mpp", SaveFileFormat.MPP);
Unfortunately, there were issues with MPP format in Aspose.Tasks, so this example will be worked starting since Aspose Tasks for .NET 19.3 which will be released in the first decade of March.