By default, jobs cleaner is scheduled to run every day to clean entities older than 30 days (the retention period can be adjusted), and only 1000 jobs are removed per execution to prevent overloading tenants with deletion jobs. Entities older than the retention period might not be removed when more than 1000 jobs are created every day.
As a solution, consider running jobs cleaner a few times a day on the tenant until it is clean. For this, request cleaning via a support case.