imperfection: Layout display was forced before the page was fully loaded

[hpvd]

with a slow connection / or throttling with devtool you can sometimes produce this warning and possibly notice the mentioned effect:

Layout-Darstellung wurde erzwungen, bevor die Seite vollständig geladen war. Falls Stylesheet noch nicht geladen sind, kann dies zu einem kurzzeitigen Darstellung des Inhalts ohne Formatierung führen.
translation: 
Layout display was forced before the page was fully loaded. If stylesheets are not yet loaded, this can lead to a temporary display of the content without formatting.

seen several times on the very first visit (no cache no cookies...) and throttling to 3G on https://demo.unpoly.com/companies