I'm sharing some troubleshooting steps to rule out any possible browsing issues. We'll start by accessing your QuickBooks Online account through a private or incognito window.
Depending on the browser you're using, these are the keyboard shortcuts you can use to open one:
Google Chrome and Microsoft Edge: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Safari: Command + Option + P
If you're able to see your customer's details, then you can go back to your regular browser and clear some cache. You can also use other supported browsers as an alternative.