Symptoms

1. You're using Documentation theme.
2. Page Tree (left navigation bar) is empty:
   
3. Instead of the page title, the browser title shows this when you browse to the dashboard: Dashboard $docThemeHelper.addSpaceName("- ", $sitemeshPage) - Confluence:
   
   
   

Cause

The Velocity Helper plugin module under the Documentation Theme plugin is disabled. 

Resolution

1. Navigate to Confluence Admin >> Plugins >> Show System Plugins, and look for the Documentation Theme.
2. Expand the Manage Plugin Modules, and enable the Velocity Helper module.