planning test session

What is your profile (access rights) ?
If you are Project Manager (or equivalent access rights), you can plan only projects you are affected to.
So planning "all project" will have no impact on projects you are not affected to (as expected), and resource planned work on these project will not be changed.

Could you try and reproduce your use case in the Demo so that I can have a look ?

In your example, A, B and C are all assigned 5 days to TS1 at 30%.
So they can work no more than 0.3 each day on TS1, and this leads to minimum duration of 17 open days.
This cannot be done from 13/02 to 06/03 (only 16 open days), and minimum end date is 09/03.
B and C ends work on TS1 on ... 09/03 : completely correct.
A ends works on TS1 on ... 13/03, which is 4 days after expected target. If you look at his planned work, you can see he is busy on 17/02, 24/02, 04/03 and 06/03 on another project, for 0,8 (and his capacity is 0,8 so he has no more availability).

So planning calculation is completely correct.
If you want to respect fixed duration (as log as possible) try and set assignment rate at 100% on the task.
The work will be dispatched as best as possible, with possibly more than 0.3 some days.

Hi,

I cannot find a case where planning priority is not respoected.

If you can set an example in the demo, please do !
(for instance with new project and new resources).

Really, take care of most important rule : if resource are shared on several projects and you don't plan all project together, exiting planning slots will not be moved, whatever the priority.
This is very important because your planning should not change planning on other project.