challenge link : https://trailhead.salesforce.com/trails/force_com_dev_beginner/modules/business_process_automation/units/process_builder . 

 in trail heads i am getting the following message "An update to an account record failed to update the mailing address fields of all child contact records. Make sure that the process is correct and that it is activated."

but when i try to manually update the account address and then check with the related contact the process is working fine there is no problem . the issue is trailhead is not accepting this solution .

P.S : i have tried deactivating all the triggers , flows , validation rules , all other stuff on both the objects . please help . !