Good morning, @NumbersByNelson. 

Welcome back to the Community! 

When you're trying to reconcile, you should only be reconciling the parent account. This could be why you're having this particular issue within your QuickBooks Online account. The software is designed to only reconcile the parent account. 

For more details about sub-accounts, check out this guide: About bank or credit card subaccount setup. 

Feel free to come back if you have any more questions. We're always here to help. Take care!