Hello,
I made the mistake of cancelling a check that I did not realize until it was too late was already in a reconcile. Even though there is a note at the top of the check screen saying “Cannot Update, GL Entry Split 635913 is Reconciled on Bank Reconcile 395” It still let me cancel the check.
Now, I cannot uncheck it from my reconcile because it is not on the screen, but it has not changed the reconcile balance, so I know it is still there.