We all know (well people who spend a lot of time on Drupal) that Pantheon have a great service. What Pantheon provides is container-ised Drupal instances, which can very easily be scaled but also maintain a separation for deployment from Dev, Test/Stage and Production. We like Pantheon so much, that we even have quite a few sites running on it. However, as it is not always exactly like running a site from a VPS it can take some extra configuration to get that up and running as you would like.
One of these areas that it can be difficult is XML Sitemaps. As a quick description of what they do, basically, they list all of the pages on your site to make it easier for search engines to know what pages your site has. You can see Will Hall Online sitemap.xml as an example of what one looks like. For building sitemaps in Drupal almost everyone uses XML Sitemap module and with 256,675 active installs and 1.2m downloads you can see it is pretty popular.
However, with Pantheon, if you turn xml sitemap on, by default, what you will get is a blank page, a WSOD (white screen of death). Now this is of no use for you or anyone else. How to rectify? There is a small setting in XML sitemap which fixes this problem:
By default this is checked. If you uncheck it, and then flush caches of your Pantheon site then your sitemap.xml will start working.
If you are looking for support for your Drupal site, then please let us know. We manage a range of different sites and are always looking for great projects to get to work on.