Welcome to the Community, @invoice1!
Let me share some insights and guide you in correcting your August 2018 accounting records.
First off, these are the scenarios that can cause a nonzero difference when reconciling accounts:
So, I recommend going through your August 2018 transactions and reading this article that discusses those scenarios and their respective resolutions in details: How to Resolve Reconciliation Differences?
If you're still unable to achieve a nonzero difference, I suggest contacting your accountant. Your accountant can help you further in checking and fixing the difference in your accounting books.
You can get back to us here in the community if you have any other concerns. We'll always be here to help.