Hi QMAXX,
I'm not really sure the reason this error is happening for the description custom field, perhaps the previous value for the default editor is empty. When I re-saved the default editor settings for description(http://take.ms/4qXil). The error no longer persists. I noticed this happens in Groups, Events, Pages and I have resaved the default editor setting in all those cluster's settings page. Double check and let us know how it goes, thanks.