It's my priority to ensure you can reconcile your transactions.
There are times when a reconciled transactions show up as unreconciled. Let's check the transaction if it's marked as reconciled (R) and posted on the correct bank account.
Here's how:
Go to the Accounting menu. Then select Chart of Accounts.
Locate the account and select View register.
Select the transaction you want to update.
Review the check column. If the transaction is reconciled, you’ll see an “R.”
If it's blank, click the box continually until the box shows the letter R.
Hit Save when done.
Once done, you can review the reconciliation page to verify if the transaction is showing. On the other hand, you can create a journal entry if the check is posted on the other bank account.
Also, I recommend consulting an accountant to ask for further guidance on correcting transactions and reconciliations to have your books more accurate.
You may visit these articles for some information about reconciliation in QuickBooks Online: