@Pascal_Netenvie make sure that you have default content of /etc/cron.daily/50plesk-daily:
# cat /etc/cron.daily/50plesk-daily
#!/bin/sh
### Copyright 1999-2017. Plesk International GmbH. All rights reserved.
# install_statistics
/usr/local/psa/bin/sw-engine-pleskrun /usr/local/psa/admin/plib/DailyMaintainance/script.php >/dev/null 2>&1
# install_mysqldump
/usr/local/psa/bin/mysqldump.sh >/dev/null 2>&1