I just ran a class report in QBO and same issue. This is not ok and should be fixed. That is the beauty of class reports. (Desktop version does this correctly.) The one "expense" item that was subtracted was actually attached to the income account.
I've got your back, sooverit2. Here's everything you need to know about running a report by class in QuickBooks Online (QBO).
When you pull up a Class QuickReport in QBO, the total amount per class item is the sum of all transactions regardless of the type. This is why you see that it adds up all the amount of your transactions and subtract only the negative one. To know more information, please check out this article: Run reports by class.
If you want to monitor the total amount of your income and expense accounts per class, you can run the Profit and Loss by Class report instead. This group all the expenses and incomes separately to easily view the totals. To do so, refer to the outlined steps provided by my colleague, Angelyn_T above. Please see the screenshot below for visual reference:

Customising reports in QBO is a breeze. This will further help you easily view the necessary details within a specified time frame. Not just that, the program also allows memorising the modification made for future use. To get started, simply click the Customise button located at the upper part of the page. 
It's my top priority to ensure all your queries are taken care of. In case you have additional questions about running a report by class or any QBO concerns, leave a comment below. I'll take every opportunity to help. Have a great week ahead.