Possible reasons for Trigger.Cron to stop firing

[David Resnick]

I opened a bug about cron triggered jobs stopping to be triggered after Jenkins has been up for a while.
https://issues.jenkins-ci.org/browse/JENKINS-25704

https://github.com/jenkinsci/jenkins/blob/84c76253862a2f36f813a7aa45b77d99c1616be4/core/src/main/java/hudson/triggers/Trigger.java#L211
The code shows a case where jobs would stop being triggered because the date on the server is changed.

Could anyone tell me of other possible reasons for the jobs to stop getting triggered?

Thanks,
David