Check for any missing email templates in each locale for your journal.
User Home → Journal Manager → Prepared Emails
Depending on your installed plugins, you should probably have around 90+ in each locale for OJS 2.4.x.
Differing counts in differing locales indicates a missing template. There are multiple forms of the REVIEW_REMIND templates: REVIEW_REMIND, REVIEW_REMIND_AUTO, REVIEW_REMIND_AUTO_ONECLICK. These also were recently broken out in to REVIEW_REMIND vs. REVIEW_REQUEST templates.
To restore any missing templates for a locale, go to:
User Home → Site Administrator → Languages → (Choose Locale) → Reload Default Email Templates