by Ken Task.
Don't speak French ... wish I did sometimes ... haven't experienced the same problem myself so this is a 'sluething guess' just looking at what it's showing in debug ...
setting_invalid_filename and it's the name of the backup file.
sauvegarde-moodle2-course-83-m2_dmse_-_ue3-théorie_des_organisations_-p4_foad-20180321-1633.mbz
The backup settings have options for what to name the backup file ... .mbz is the extension. so in those one could opt to use course shortname, etc..
I see a 'é' in the backup file name which should be ok, but the other items that involve a '-'?
'_-_' and '_-p4' ...
what if you changed the shortname/longname of the course removing the "spacedashspace' or 'spacedash' in front of p4 - in other words ... remove the dashes and use only one space.
'spirit of sharing', Ken