Assuming you are connected to the internet with Haste installed properly, one reason your Haste Pro subscription would stop working (meaning, your optimization isn’t working) would be a payment failure.
We will always notify you by email more than once if there’s been a payment issue, but you can also check your subscription status at My Account. If your payments are current but you’re still having issues, please contact us by submitting a request at support.haste.net or sending us an email at support@haste.net.