I struggled with this same issue for months along with notices that employees were missing information when they weren't.  I finally realized that my work location address had the wrong zip code and was not valid.  Double check your work address for each employee and make sure it is valid. You may want to use the USPS validation to make sure.

Also, with Quickbooks Online Payroll Core, you cannot edit or delete work addresses.  You have to go to an individual employee "Employment" tab and under work location select "New Work Location" to add a new one with the corrected address.  Apparently you can contact support directly to have the old invalid address removed.

It would be really nice if Quickbooks had an actual address validation and prevented this from happening.