#app-navigation-toggle missing

[ChristophWurst]

Steps to reproduce

1. Install an app that does not render it's full structure right away on page load (works with Mail v0.12.0-RC3)
2. Load the page with a bandwidth throttler (from the FF dev console for example) with a mobile resolution (narrow screen)

Expected behaviour

See the #app-navigation-toggle injected (a burger menu to toggle the navigation on mobile) as documented at https://docs.nextcloud.com/server/15/developer_manual/design/content.html

Actual behaviour

See no icon

Server configuration

Nextcloud version: 15 & 16

cc @nextcloud/javascript

[ChristophWurst]

Contacts show the content details right away: no problem
Mail starts with a loading screen: 💥