Usually, this error occurs when there's too much cache in your browser. To fix this, let's perform some browser troubleshooting steps. Before doing so, make sure that adobe reader/acrobat is updated to the latest release. Here's the link: How to update, repair, or re-install Adobe Reader/Acrobat.
Let's start by opening QuickBooks Online (QBO) through an incognito window. It's the best place to identify web issues. Here are the keyboard shortcuts:
Google Chrome: press Ctrl + Shift + N
Mozilla Firefox: press Ctrl + Shift + P
Safari: press Command + Shift + N
If you're able to see the sub total amount using the private window, go back to the regular browser and clear its cache. We advise customers to clear them out periodically to prevent and fix web issues. You can also try using a different browser. Here's the link: System requirements for QuickBooks Online.