When a bank feed is reconnected, QuickBooks Online (QBO) attempts to re-establish the link between your bank account and the account register, which can lead to the issue you're experiencing. Collinm.

During this process, QBO automatically downloads your recent transactions to ensure your records are up to date. This action may create duplicate entries, like Opening Balance from Bank. If there is a transaction like the opening balance in the initial connection, the system may retrieve it again during reconnection and mistakenly treat is as a new one. 

Since this transaction isn't showing in your bank register, you can drill down your transactions through the reports by clicking on the duplicate. This will take you to the actual transaction details, where you can verify whether they are indeed duplicate which showing on the same account and confirm if they need to be deleted. You'll want to delete if the transaction isn't necessary.

As a reference, I've added a screenshot below with a green box highlighting where you can click the amounts. This will allow you to drill down into the transaction details directly and verify the information thoroughly:

Another possible reason for this issue is when you use a bank rule, which is set to automatically to categorize transactions once they are downloaded from your bank. If the rule misapplies or duplicates certain transactions during the download process, it could lead to this discrepancy. To prevent this from happening again, double check if a rule is correctly set up. To do so, follow the steps below:

1. Go to the Gear icon and select Rules.
2. Double-check the rule or you can click Delete if this isn't needed.
    

Let me know if you need further assistance with your bank feeds or anything related to your bank balances. We're always right here to help you.  Have a nice day ahead.