Regression: Author can't see channel in Channel Manager

To reproduce:

• Log in as author
• Go to the channel manager
• Open a channel
  Expected result: The page is rendered in the Channel Manager
  Actual result: The channel manager is not rendered at all (white screen)

There is a JavaScript warning:
Ignoring toolbar plugin 'org.onehippo.cms7.channelmanager.templatecomposer.deviceskins.DeviceManager', unknown neighbor: 'template-composer-toolbar-fullscreen-button'. Known neighbors are:
(page-editor-all.js:2961)