Shipping rates error

Hi,

Some of my customers have not been able to select shipment options for their orders.

The error on my end is this:
12-02-2018 @ 19:02:55 – Error. Unable to get shipping rate(s) for wc_services_usps instance id 3. (check_and_handle_response_error)
12-02-2018 @ 19:02:55 – nothing_to_ship No shipping rate could be calculated. No items in the package are shippable. (check_and_handle_response_error)

I have seen this error many times, but not all customers get it.

I have only 4 items, all of which have shipped multiple times. They have defined sizes, weights, etc.

Can you please advise?

My website is HeyHealthJunkie.com.

Thanks,
Nicole