After performing a condense, the reconciliation beginning balance changes.
When choosing the options for condense, the option for Uncleared (unreconciled) bank and credit card transactions was checked.
QuickBooks also removes transactions prior to the Remove transactions before date that may have been reconciled. Since both cleared and uncleared transactions are removed and a summary entry is created and cleared in their place, the beginning balance (which is the sum of all previously cleared transactions) is altered.
If you want the beginning balance to not be affected, you will have to restore the backup that was created prior to the condense. You will then have to perform another condense, not selecting the option to remove Uncleared (unreconciled) bank and credit card transactions.