Thanks, @JamesLE
Were there any changes in how you return the certificate filed in the new order response?
https://www.rfc-editor.org/rfc/rfc8555.html#section-7.4
“valid”: The server has issued the certificate and provisioned its URL to the “certificate” field of the order. Download the certificate.
We used to read that field, but it's no longer working. We just switched to read the location res header instead and that appears to be working