There's a discrepancy because at least one transaction was changed or deleted after it was reconciled.

Hi kudosamen-gmail-,

It's a pleasure to see you in Community.  Welcome!  It's essential that your accounts remain balanced in QuickBooks Online.  I'd be happy to help!

Changes that have been made after an account has been reconciled can have a negative impact on other areas of your books.  To review the items that have been changed or deleted, go to your Settings ⚙, in the top right of your QuickBooks dashboard, then select Audit log.  If you see that an item was deleted, this can't be undone.  In this situation, you'll need to re-create the transaction in your books.

If you'd like additional assistance with the process, please don't hesitate to contact us.  We'd love the opportunity to work with you directly and get you back to business as soon as possible!

Schedule a Callback or start a Chat: click (?) Help in the upper right in QuickBooks Online > enter "Contact support" > hit Contact Us > provide a brief summary of your situation > hit Let's Talk > choose Get a callback or Start a Chat.
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Feel free to reach back out if any other questions come to mind.  We'd be glad to assist!