offline-plugin: Plugin's runtime wasn't added to one of your bundle entries.

Besides adding the plugin to the config, the runtime should be included into an entry of your project (typically main entry). This error happens if you forget to do that. If you indeed added the runtime and this error still happens then please file an issue describing what happened.

Runtime can be added to the project this way (don't forget to call the install() method):

require('offline-plugin/runtime').install();