I am running DNN 4.9.4 and unfortunately I had my coder create a module which uses the scheduler heavily.  What I have found is that it works for awhile and then:

The scheduler "next" times freeze in the past and so are not run again (disable and enable doesn't fix it)

It's very frustrating.  Has this been fixed in a later version and, if so, can somebody point me toward a resource that explains how it was fixed?  I don't want to upgrade my site unless I know the scheuler has in fact been fixed and I will no longer have these problems.  I wish I would have known about the scheudler limitations prior having these modules constructed but live and learn.  Thanks for any help.

Thanks Mitch...I'll take a better look and get back to you.

I am having the same problem with Active Forums mail retrieval task. - it gets run more than once.  I have the interval set to 5 minutes and you can see in the history that it is being started and then started again 1 minute later, which causes it to fail (POP3 server doesn't like the multiple requests).

I'm running DNN 5.1.4