The APM plugin adds a link to Upgrade Assistant to the help menu (see here). The Upgrade Assistant can be hidden from the UI (without disabling the plugin) with the config xpack.upgrade_assistant.ui.enabled: false. We also plan to add a config to disable the plugin completely xpack.upgrade_assistant.enabled: false.
So the help link could lead to a hidden/disabled plugin. I think it should check if UA is available first before adding it.

Screenshot