Hi Séverin, sorry for the lack of information!
We have 3.3 version and in a course some of a multiple teachers deleted an assignment activity that included dozens of files (.pdf and .docx) that students had submitted over a few weeks. The students are still in the course. We couldn't restore that activity from recycle bin since it had been deleted over a week ago (7 days is the default setting in Moodle) and actually we realized that even if you restore the activity before that 7 days has passed it deletes all submitted files from the activity immediately when you click delete. To test this we created a new assignment activity and submitted some files to it. Then we deleted it (edit -> delete, confirm: yes) and after that we clicked restore from the recycle bin: all files that were submitted vanished.
So my question is basically that is there any way to restore the submitted files in activities such as assignment if this happens? We managed to find some of the files from backups but there was a one week gap in backups since it had been over a week that the assignment had been deleted. I also tried to find settings regarding recycle bin or restoring files inside activities but didn't find any.