I had that happen on one account (also a credit card account) - the account balance a couple years back in the reconciliation history was suddenly off by a large amount and then was back to the correct value about a year later. I couldn't find a way to fix it other than to completely clear out the reconciliation history & rereconcile the account from scratch using the most recent statement. I lost all the reconciliation history but the erroneous reconciled balance was gone.
You don't need anything other than the most recent statement.
When you're looking at the reconciliation history window, click on the Clear History button in the lower left. This will remove all reconciliation for the account & every transaction that was marked Reconciled will be changed to Cleared.
Then exit the history window to go back to the reconciliation window. Perform a new reconciliation using the balance & ending date for the most recent statement. Click Next and you'll be performing a reconciliation but for the entire lifespan of the account. You might have to select or unselect a transaction or two near the statement end date (as per usual) but you should be very close to balanced already. Once you've zeroed out the difference, hit Finish and you're done. All the old transactions are reconciled again.
I'd back up your file before doing this just in case something goes wrong.
@Jon @verso21 I've run into this type of problem before as well, and it frustrated me that Quicken doesn't have a way to delete one month, or a few months, of reconciliation history in order to re-reconcile to resolve a discrepancy which spans multiple months. As @Jon noted, it's possible to “Clear History” to delete reconciliation history for all time, and then do one mass reconcile of everything up to current time, but this presents a sledgehammer solution to problems which might require a simpler, smaller fix. So I created an Idea thread to request the addition of a feature to allow individual reconciliations to be deleted, without losing the entire history of reconciliations.
Please take a few seconds to visit this topic, add your vote, and add your comments.
Vote and comment here: https://community.quicken.com/discussion/7930438/allow-individual-account-reconciliations-to-be-deleted
I've deleted the reconciliation for one of my credit cards a couple times now & was able to do a fresh reconciliation both times without getting the re-reconciliation window. I don't know why it's working differently for you.