I had a similar problem here while trying to test sending messages using a template with Marketing format.

Messages using templates with Utility format were being delivered while messages using templates using Marketing format were not.

Turns out WhatsApp limits the number of Marketing messages a number can receive. You can only send more marketing messages if the user replies to the first or second message.

After I replied to the last message, the new messages started to be delivered again.

For more info: https://developers.facebook.com/docs/whatsapp/cloud-api/guides/send-message-templates#per-user-marketing-template-message-limits