Since background jobs are initiated by the job scheduler supplied by the RDBMS, you need to ensure that the scheduler for your specific RDBMS is properly configured.
With Oracle: P6 EPPM uses DBMS_SCHEDULER to schedule background jobs with Oracle.
With Microsoft SQL Server: P6 EPPM uses the SQL Agent service to automatically schedule background job execution with Microsoft SQL Server. Background jobs handle the maintenance of the utilities tables (for example, USESSION and REFRDEL). As a part of background jobs, the agent runs the SYMON and DAMON stored procedures at specific intervals.