well... I didn't expect any answer... but to close the issue... I think there is a bug somewhere here (maybe in wherenotexists )

I changed the query to something equivalent to make it work

return DB::table('contact_emails')
		 	->join('user_contacts', 'contact_emails.contact_id', '=', 'user_contacts.contact_id')
			->where('user_contacts.user_id','=',1)
            ->whereNotIn('contact_emails.contact_id',function($query)
            {
                $query->select('event_contacts.contact_id')
                      ->from('event_contacts')
                      ->where('event_contacts.event_id','=',17);
			})
			->get();