If any of your custom post type page (events, sermons, staff, etc.) returns 404 “Not Found” error when opening single details page, follow below measures to fix it:

1. Visit page at Dashboard => Settings => Permalinks and click on the “Save Changes” button.
2. Try disabling all your plugins to check if any of them is not conflicting with the installed theme.

If this doesn’t help, please submit a support ticket.