You say the domain was marked as clean by the Spark folks.
I wonder if something happened to flag it again. For example, when you send emails from your laptop are you using the same server as the one your shop uses? If not, and you have DKIM key declared, are both servers specified - as in one is sending signed messages, the other is not so any receiving server gets confused with the number of signed/non-signed messages? Is the SPF text correctly listing all servers used?