Symptoms
You have activated ServiceMapping plugin but the service mapping home page is blank.
Cause
You might still be using UI15 and not UI16
The UI16 plugin is not active.
There is a dependency for Service Mapping home page with UI16.
Resolution
Activate plugin : "com.glide.ui.ui16"
If this is a non-production instance, with admin role you should be able to activate it yourself from the plugin list.
If this is production, you will have to put in a HI request to have that plugin activated.
Additional Information
Activating this plugin automatically forces all end-users with exception to admin users to use the new UI.
If you need to prevent this you will have to create a property and set it to 'public'. This will not prevent end-users from not getting the new UI, but it will give them the option to switch back to UI15.
See here for more details on the property: