I've received the replacement unit. Now Kalman is working properly.
I just have other issues.
First I got a problem with the RTC. I connected the VDDRTC to a powersource to be able to save time from being erased when I turn off the system.
If I understood, to get time to work infinitely, i have to set the configuration register's first bit CONFIG to 0. But when I reboot the system, time resets to 0.
The second problem is related to the acceleration. I want to get rid of the gravity component, so I set EKF_CNFG to 1 as discibed in the datasheet. I am in the body frame and want to get the acceleration to try use it in a dead reconing process in order to get the position of my device in its reference frame. I get exactly the same output as when Idon't remove gravity (ie. 1g on the z axis when the device is put on a flat table).
In fact Ii works when I am in Navigation frame but not when I am in Bodèy frame.