In the settings_navigation_ajax->initialise() method, the $this->context is not set like in the parent method. This causes a problem once settings_navigation->load_local_plugin_settings is called and $this->context is passed to local plugins which then pass it to capability methods. The capability methods throw exceptions if the context is null.

In addition, ajax_check_captured_output is a little sensitive as it prevented the admin menu from opening because of a single space character. Usually these characters are a result of a space after a ?> tag. Due to the size of Moodle, these are almost impossible to find. Let's have ajax_check_captured_output trim the buffer so it only errors out when something substantial is printed.