I appreciate you for reaching out to us here in the Community. I'm here to help you fix the bank balance in QuickBooks Online.
Since you already tried reconnecting your PayPal account, but the issue persists, the browser's stored cache may be full. It can cause unusual behavior in QuickBooks Online (QBO), such as showing incorrect bank balance.
I'd first recommend signing into your QBO account using a private browser. It doesn't store data in the cache. Thus, it's a great way to isolate browser-related issues.
If you're using Mozilla Firefox or Microsoft Edge, press the CTRL + Shift + P shortcut on your keyboard. For Safari, hit Command + Shift + N. Press CTRL + Shift + N if you're using Google Chrome.