Check the number of scheduled backups:
# plesk db
mysql> select d.id as 'Domain ID',d.name as 'Domain name',c.cname as 'Client Name',bs.obj_type as 'Backup type',bs.repository as 'Destination',bs.last as 'Last time',bs.active as 'Status',bs.backup_time as 'Time',bs.content_type as...