I appreciate your efforts in trying some steps to get this this issue sorted out, @Gabymaz. I’ll be here to lend a hand with making a class inactive in QuickBooks Online.

First, let’s check what option have you selected when assigning a class to a transaction. If you’re using One to each row in transaction, you can change it into One to entire transaction. This way, you won’t need to track each of them.

Here’s how:

1. Go to the Gear icon and select Account and Settings.
2. Navigate to Advanced then Categories, and click the pencil icon.
3. Under the Assign classes, choose One to entire transaction.
4. Select Save then, Done.

 
Once done, you can then make the class inactive. By doing this, it will still show on your reports as long as there are transactions associated with it. I'll show you how:

1. Navigate to the Gear icon and select All Lists.
2. Tap Classes.
3. Find the class you want to inactive.
4. Select the dropdown arrow ▼ next to Run report, then Make inactive.

If the issue still persists, I'd suggest reaching out to our QuickBooks Online Support. Just make sure to check our support hours so you can contact us at a time convenient to you. This way, we can address your concern on time.

Considering that your concern might require an exchange of account information, we can’t have them posted here for safety and security purposes. They have the tools to investigate what's causing this behavior and work with our engineers to get the error fix.

Please let me know if the steps above do the trick. As always, I’d be glad to help you further with managing your class. Keep safe!