You are creating an invoice for item fulfillment and tax is not calculating. However, only when the invoice is edited and saved is tax generated.
Ensure you are not using User Event script for a custom function.
- Script 'NS|Auto Create Invoice' is of type User Event. Avalara script which is used for tax calculation on invoice is also of type User Event. As per NetSuite architecture, User event script cannot be executed by other user event script. See screenshot from NetSuite help center for reference.