I'm running into an issue where Magento is not sending the shipment confirmation email after I enter the shipment for an order. I've tried entering the shipment in the Admin page, and also entering the shipment through the API. In both cases, the shipment confirmation email is not sent after the shipment is entered. I do have "Shipment" emails enabled under Stores > Configuration > Sales > Sales Emails.
If I go into the Admin page, go to Sales > Orders, pull up the shipment, and then click "Send Tracking Information", the email is sent.
When I place an order, the order confirmation email is sent correctly.
When I invoice the order, the invoice email is sent correctly.
Why are the shipment emails not being sent when a shipment is entered?