I've come to help, @LaurieDeCarlo.

Thank you for giving information about your concern and for following the steps recommended by my colleague. To isolate the issue, I suggest checking the transactions that appear to have no class in the report. Make sure there is a class assigned to the Class column for the item. For more details, please see this article: Set up and use class tracking in QuickBooks Desktop.

If the issue persists, I recommend reaching out to our technical support team. This way, they can further investigate why your class field is blank when running a transaction report. They also use specific tools to do a screen share to check your set-up. 

Here's how to connect with them:

1. Go to the Help menu and choose QuickBooks Desktop Help.
2. Click Contact us. 
3. In the Tell us more about your question box, enter Class field is blank when running Transaction by detail report. 
4. Hit Search.
5. Select Start a Message. 

Also, personalizing your report in QuickBooks is a breeze. For the detailed guide, please see this link: Customize customer, job, and sales reports in QuickBooks Desktop. 

Let me know how this goes and leave a reply below if you need further assistance running a report by class. I'm always around to help. Have a good one.