Hello, Johnny Zhang. 

I'd be happy to help you with showing the quantity/rate on your Purchase Order in QuickBooks Online. 

Performance issues in QuickBooks are resolved by doing basic troubleshooting steps. Let's start by opening a private browser to start a new session.

Here's how to open a private window in different browsers:

• Google Chrome: press Ctrl + Shift + N.
• Mozilla Firefox: press Ctrl + Shift + P.
• Safari: press Command + Shift + N. 

If you're able to view the quantity/rate on your Purchase Order using the private browser, let's go back to your regular browser and clear its cache. You can also do this task on other supported, up-to-date browsers. Clearing the cache will refresh the system, and you'll be able to work with clean trash.

You may find this article helpful: Create and send purchase orders in QuickBooks Online.

If there's anything else you need or you have other QBO questions or concerns, just leave a comment below. I'll be here for you. Stay safe!