I would look in the basecode for any custom clietlib that might extend core functionality by using one of the AEM's clientlib categories, like cq.authoring.editor.* or granite.ui.*. Maybe you have some clientlib that interferes with ootb clientlibs abdbreaks something.
@rosudel Did you find the suggestions helpful? Please let us know if you require more information. Otherwise, please mark the answer as correct for posterity. If you've discovered a solution yourself, we would appreciate it if you could share it with the community. Thank you!