Hi Sami,
it seems that the loading and initialization process in the browser can run into a timing problem when the page is more complex and has several editor fields.
I had to edit the CKEditorService::loadEditor method and surround it with a try-catch because sometimes the $wnd.CKEDITOR was still undefined and the thrown exception stopped the addon to work completely. I had to close and reopen the browser tab to get it working again.