OK, I logged into Seahub, went to the library and then displayed the history using the clock icon.
Here is what I've got :
As you can see, there are not much details : the deletion happened in the "Détails" event.
I am supposed to be the user responsible for all thoses events...
When I click on details, I have all the modifications listed :
* Two subfolder and their files marked as new (which they are not)
* A lot of deleted files, which I didn't delete
* A modified file that I don't believe to have modified at this time of the day
* 5 subfolders deleted, which I'm sure I didn't delete
Only two accounts have access to this encrypted library and the other person didn't make any change at this time.
This morning, a third machine with the other account and Seafile Client 6.1.3, deleted the content of a folder.
There was no user on this machine at this time...