Thanks a lot, I tried that but then when I move the milestone to the right for example, then indeed Subtask1b is properly "shifted" to the right, but Subtask1a remains in the same position... I would like Subtask1a to also move respectively to the right.

I attach a test.mpp. In this example, if the milestone moves, then subtasks "Pre-Checks" and "Backup" stay static although I would like them to also move. Probably my dependencies there are not ok.. I would appreciate some help, I have been struggling with this for so long!