Hello ShawnSheng,
Thank you for your question.
There might be possibility that the account with which you connect to Azure does not have access to that subscription so it does not sees it at all. Usually when you create Automation Account via Azure Portal RunAs account is created. That RunAs account is actually a Service Principal that is assigned Contributor access but only to the subscription where the Azure Automation account is created. If you have other subscriptions you have to assign access manually or create Automation account in each subscription.
Please check if you correct permissions with Automation Account or should have a access as a contributor on your storage account.
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