Installation triggers WSOD error on Pantheon

When enabling the module on a Pantheon environment, I get the following fatal error:

Symfony\Component\Routing\Exception\RouteNotFoundException: Route "site_map.settings" does not exist. in Drupal\Core\Routing\RouteProvider->getRouteByName() (line 191 of /srv/bindings/e9ea916135c949a1ab0a35aa269ff3a5/code/core/lib/Drupal/Core/Routing/RouteProvider.php).

This only happens the first time the page is loaded after the form is submitted -- upon subsequent visits to the page, the module is enabled and the Configure link can be used.

I am assuming it's PHP version; I'm running 5.6.8 locally, vs. 5.5.24 on Pantheon. My local webserver is Apache/2.4.16 (Unix) vs. Pantheon's nginx/1.4.7.