Please know your feedback on the changes made within the program is valid, @RobbinN. I recognize your concern about populating the email address on the invoice for a customer project, and I'd like to point you to the support who can assist you.

In QuickBooks Online (QBO), once you've entered the email address on the project or customer's profile, it will automatically populate once you create an invoice or other transaction.

As it is unexpected for the email address to show on the invoice and then suddenly disappear, I recommend contacting our Customer Live Support team to investigate it further. They're fully equipped with tools to pull up your account securely and conduct an inquiry to identify the cause and provide the best solution.

Here's how you can reach them:

1. Go to the Help menu, then select the Search tab.
2. Click Contact Us.
3. Choose a topic, then enter a brief description of your concern and hit Continue.
4. Pick either Chat with us or Have us call you and start connecting with them.
   
   

For additional reference, you can use the following article to personalize invoices in QuickBooks: Customize invoices, estimates, and sales receipts in QuickBooks Online.

In the meantime, if any other concerns arise or if you have additional questions, please don't hesitate to add a reply below. I'm here to ensure you'll receive the help needed.