Error: Branding Settings are not returned by the Channel’s List API. Causing the YouTube channel header banner and video slider not to load.
This functionality (fetching brandingSettings via API) has been down since about 1am Aug 28, 2018. Hopefully someone from YouTube sees this and fixes soon, it has been reported. Things similar to this have happened in the past and usually fixed within a day or two by the development team over at YouTube HQ.