Hello, Singyin. 

To isolate the issue, I'd like to make sure this isn't a problem with the browser. Let's perform some troubleshooting steps to resolve this issue. It's possible that the browser stores frequently accessed data, thus causing websites, like QuickBooks, to act weirdly. Let's try logging into your QuickBooks account using the private browser. 

You can access this by pressing the following commands:

• Ctrl + Shift + N (Google Chrome).
• Ctrl + Shift + P (Firefox or Internet Explorer).
• Control + Option + P (Safari).

If it works, then let’s go back to your browser and clear the cache. These caches of data are essentially junk files and can be safely deleted to free up storage space.

If the same problem occurs, try using a different browser. This can be an issue with the browser that you use and QuickBooks.   

You can also check this article for more information about credit notes: Create and apply credit notes or delayed credits in QuickBooks Online. 

Feel free to leave a comment below if you have a follow-up concern in your account. I'm always here to help. Take good care always.