Hey PKP,
only in case if you have missed it: like in the previous OJS 3 version, there seems to be a problem with the external feed plugin on the site-level also with the new OJS 3.1 release.
(see: External feed plugin on site level ins OJS 3.0.2)
A fatal error on site-level appears (blank page) when the external feed plugin is enabled: ´"Fatal error: Call to a member function getId() on null in /data/ojs/ojs-toe-31/plugins/generic/externalFeed/ExternalFeedPlugin.inc.php on line 149"
Only disabling the plugin helps here 
best regards,
Tahsin