This behavior is similar to the one I had previously reported about project templates, which as soon as they are copied, lose the initial organization of the timeline:
I hope you will offer an update quickly because these points lead to a need for reorganization of tasks very frequently unfortunately.
To add to this, there are some other frustrations with the way that Asana auto-arranges tasks on the timeline.
If you add something to the project timeline, it seems to always create a new row in that section just for that one task. What that means is that, over time, each section becomes huge and it’s impossible to view all sections of your timeline in a clear and condensed way.
That means that I now have a daily task of going in and manually dragging and dropping tasks around to condense the sections back down. It’s not the best way of spending my time.