Hi Leah,
It may be that the Authors simply aren't using the email notification option after they resubmit/revise their submission. If you take a look at Figure 5.3.1 here:
http://pkp.sfu.ca/ojs/docs/userguide/2. ... eview.html, you'll see that there's a Notify Editor email icon available to the author; this is the only notification option at present, ie., there is no additional email notification that the author will receive automatically on file upload. There *should* be a notification option available for editors to receive notifications on the submission of any new revised file, but there currently isn't; I've submitted this as a feature request
here. Please feel free to CC yourself to that report for future updates. And until then, your best bet may be to modify the "EDITOR_DECISION_REVISIONS" prepared email to include specific instructions to the author to use the notification email when finished revising the submission.
Cheers,
James