thanks! i found the error!

during development i did change the name attribute in the bower.json, but not the component attribute, which lead to 2 components having the same attribute. the course/en/components.json is using the component attribute as identificator, so it had found 2 components and threw the error.

the solution was to delete the unused plugin according to the FAQ:

https://github.com/adaptlearning/adapt_authoring/wiki/FAQ#hdap