Drupal 7 views Contextual filters with Page & Blocks
Contextual filters works well for any display type that has a path. A path makes it easy for views to determine what information should be passed into the contextual filters.

The problem with blocks is that they don't have a path. Views does not look at the current url and automatically pass values to the filters because it has no idea which parts of the url to use.

You can get around this by using Default Values (or page manager/panels, but that's a whole other topic).

In the settings for your block contextual filter, you will want to override the configuration and select Provide a default value. Under type choose Raw value from URL and set the Path component to 2 (the path component will be different depending on your URL, but for domain.com/items/node-title the component is 2)



When you assign your block to a region, you probably want to set the allowed paths so this block won't show up anywhere else. The path component is "hard coded" so if your path ever changes you will need to adjust it.