I’d be glad to help and get to the bottom of this.
There’s a possibility that one of your users deleted the invoices. Thus, you’re unable to view it. Let’s check your Audit log and verify this. There, you can see who made those changes and what they did.
Let me guide you how to do it in your QuickBooks Online (QBO) account:
Go to the Gear icon.
Select Audit log.
Use the fields on the Filter panel to choose the appropriate User, Date, or Events filter to narrow the results.
Thick the Show only these events option and mark the Transactions box.
Choose either All Transactions or Deleted/Voided Transactions from the Show field.
Then click Apply.
Locate the deleted invoice and click the View link under the History column to open the invoice.
If you’re unable to view it from your audit log, you’ll want to ensure you’re accessing the correct QBO account. It could be you're accessing the wrong account. Thus, you’re unable to see those invoices.