set404Override and debug toolbar

Anyone else able to get the debug toolbar to show on 404 overrides?

$routes->set404Override('App\Foo::bar');

Debug toolbar shows on every page in 'development' environment EXCEPT the App\Foo::bar override

Note: Toolbar is displayed when accessing the same route via the /foo/bar in the browser.

CI_ENVIRONMENT and CI_DEBUG at Foo::bar echo 'development' and 'true' as expected.

Even tried passing debug to view('foo_bar', $data, ['debug' => true]) with no change.

Running out of ideas, sans modifying core files, which shouldn't be necessary.

CI Version: 4.1.3

Thoughts?