Why some scheduled jobs were not launched?

Since 2009 we have had incidents that scheduled job failed to launch at night. Totally we have 447 jobs failed to launch among 365981 jobs a year. Even though the fail-to-launch percentage is as low as 0.2% it is still important to know why it happensWe have many jobs in scheduler and most of them are Batch Posting which runs on single-threaded job queue every 5 minutes - which is not critical as the next run will post the rest batches.  But some scheduled jobs are for sales invoice printing and sales updates and we have to manually run them if auto-launch fails.
We tried to analyze to find any pattern to see if the fail-to-launch has common things like server, job queue, object name but we were not able to find any. We also submitted a service request to Oracle Support but there was not suggestion provided.