I appreciate your prompt reply and for sharing additional details of your concern, @norstar.

Let's access your QuickBooks Online (QBO) Advanced in a private or incognito window and do a backup from there. This way, we can check if this issue is caused by stored cache data from the browser.

The browser saves data files to swiftly load web pages faster the next time you visit them. Too much of it causes unusual behavior and affects the performance of your account. Using a private window helps us verify the issue as this doesn't store any cache and cookies.

You can refer to these keyboard shortcut keys in opening a private window: 

• Press keys: Ctrl + Shift + P (Mozilla Firefox & Microsoft Edge browsers)
• Press keys: Ctrl + Shift + N (Google Chrome browser)
• Press keys: Command + Shift + N (Safari browser)

If you’re able to back up your company, I’d propose clearing your regular browser's cache to refresh the system and start with a clean slate. If the issue remains, I recommend using other supported browsers. This way, we can see if this is a browser-integrated issue.

You might also want to utilize this article for reference in case you need to export your data from QBO: Export Data out of QuickBooks Online.

I'm always ready to help whenever you have other queries about backing up your company file. Keep safe!