I've been entering expense transactions and all of a sudden all of the names in the category column are not showing up from all of my transactions from the last year

There are instances that an issue like this occurs when the system encounters browser-related issues,  suzannebenmenach.

We can fix this by opening QuickBooks on a private window. It is the best place to identify browser-related issues.

You can use these keyboard shortcuts to open one depends on your browser:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Microsoft Edge: Ctrl + Shift + P
• Safari: Command + Shift + N

If it works, you can go back to a regular browser and clear its cache. A piled cache can also be the reason for some unexpected issues on the system.

You can also switch to a different supported-browser like  Google Chrome, Mozilla Firefox, Safari, or Microsoft Edge.

I've also added this reference as your guide in managing expenses: Enter and manage expenses in QuickBooks Online.

Let me know how these steps work on your end. Keep safe!