manual planning & planning calculation

Hello team.

I'm trying to adjust end date of a manual planed task.
There is no assignement, the predecessor is closed, and i do not modify the start date, only the end date to adjust duration.
I ran planning calculation. Others task correctly adjusted but not this one.
AFAIK there are not other constraints on this task.

Is there any way to view some sort of calculation trace to see what could be the cause?
Thank you for your great support

Thank you for your reply and help.
Does this mean an assignment is mandatory to a manually planned task?
I just would like to manually set start date and end date to this task which represent a given period of time, but with no assignment on it.

Thank you for you reply.
Unfortunately the only way to modify duration -- and end date -- in my case was to drag the bar on the gantt chart. And this, whatever scheduling options i choosed. Then, the dates within the activity, and the gantt reflected correctly the given date/duration.

btw, thank you again for your support.