Hello there, @erica.bonnette-l. I’ve got some troubleshooting steps for you to perform to sort out this issue of being unable to create customer statements.

Too much historical data from the browser causes discrepancies that affect the view and performance of your accounts. It might be the cause why you’re unable to create your customer’s backdated statements.

For us to determine if this is a browser-related issue, I suggest using a private or incognito window. To save you time, use either of these keyboard shortcuts depending on your browser:

• Ctrl + Shift + N for Google Chrome browser
• Ctrl + Shift + P for Mozilla Firefox & Microsoft Edge browsers
• Command + Shift + N for Safari browser

Then, perform the same task again. If it works fine, you can go back to your original browser and clear its cache to start fresh or use another supported and up-to-date browser to narrow down the results.

Once you’re ready, here’s an article that can help you send and show customers summaries of their invoices, payments, credits, and balances: Create and send customer statements in QuickBooks Online. 

Fill me in if you have more queries about creating statements in QBO. I'd be glad to assist you further. Take care always, and have a pleasant day ahead.