Following points have been seen on information panel : 

Point 1 : 

When a file is added for the first time, it is automatically set as updated in activity flow. 

Is it ok (since it has not been updated, juste loaded one time) ? 

Point 2 : 

When a file is edited and updated, activity flow is not automatically updated : we have to select another file, and to come back to file in order to see that file has been edited. 

Point 3 : 

When a file has been edited and updated, there are 2 different information about update date (see below). Update date in activity flow is correct.