Graphs aren’t displayed if you use Piwik Mobile 1.5 or earlier. Please update Piwik Mobile and Piwik server to the latest version.
If you still don’t see any graphs in Piwik Mobile ask your Administrator to open the Piwik “Plugins” page which can be found under Administration top menu link. Make sure the
ImageGraph plugin is activated. Within the description of the plugin there is also a link to verify graphs are working. Just click the “Debug: All images” link. If graphs are not displayed there, the error is caused by your Piwik installation and not by Piwik Mobile. Make sure all required extensions are installed for example the GD extension.
There may be also an issue under Android when the webserver uses gzip to deliver the images.