Thanks for keeping us updated, Brp. 

We're unable to automatically sync the invoice number on the Estimate once you've created an invoice from it. I also checked our list of reported issues and didn't find similar ones. For now, when you open an Invoice linked to the estimate, you'll see an Estimate summary box below the Invoice page. The estimate linked to it and other Invoices made out from the Estimates (progress invoicing) are also shown there. You can refer to my screenshot below.

You can also pull the Estimate and Progress Invoicing Summary by Customer report to view invoiced amounts, and remaining amounts to invoice. 

I'll be here if you need anything else. Thanks!