Online balance does not agree with bank since R47.15 update
how's the original Quicken Opening Balance of the accountQWin Deluxe Subscription - Win100
Note that the Online Balance is downloaded from the financial institution and can't be changed. If it is really wrong then you will have to switch to reconciling to the “statement” instead of the online balance. Note that the “statement balance” you are reconciled is just a number you type into the dialog so you can actually reconcile to a balance you get off of the financial institution's website for a given day.
On the other hand if it is the “Cleared Balance” in the Reconcile dialog that is off then that is a calculated balance based on the reconciled and cleared transactions in your register. And if it is wrong you have to find the transaction(s) that are wrong, and as @Ps56k2 points out it might be that Quicken changed your Opening Balance (it is common bug).
You should also state which financial institution this is because various ones have problems with the Online Balance.Signature:
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