When you type in 'Plugins' in the Filter Navigator, and then click on Plugins, you get Page Not Found.
Any starting with New York
The plugin, 'Unified Plugin Experience Client', is not activated on the instance.
1. In the filter navigator, type in 'v_plugin.list', which will bring up the list of plugins.
2. In the ID field, search for 'com.snc.unified_plugin'
3. Open the record and click 'Activate/Repair'
Now try to access the plugins from the Navigation Menu, and you shouldn't get the Page Not Found error anymore.