We haven't received any queries from other customers, like you, with postings that didn't show up in reconciliation. In QuickBooks Online, transaction listed ready for reconciliation is based on the date and their posting status.
With this, let's consider pulling up your account register and determine the transactions you needed to include in the current reconciliation session. You can do so by following the steps below:
Go to Accounting.
Select Chart of Accounts.
Find your bank account from the list of accounts.
Under ACTION, select View register.
Review your transaction including the date.
On the Check column, make sure the status is correct.
However, I'd still recommend contacting your accountant for guidance with your reconciliation. If you haven't yet, here's a link you can use to find a bookkeeper near you: Business is better with a ProAdvisor.
Don't hesitate to post again here if you have other questions or concerns with QuickBooks tasks and navigations. I'm always around happy to help. Stay safe and have a good one!