CKEditor crashes when switching text format for specific content types
I would "downgrade" to the stable WYSIWYG 7.x-2.2 version of the WYSIWYG module, and to the 3.6.x version of CKEditor (such as CKEditor version 3.6.6.1.7696), since the WYSIWYG module does not support the 4.x version yet ...).

Another option is to switch to the CKeditor module (which is in core in D8 now ...), and no longer use the WYSIWYG module in combination with the CKEditor library.