Did you try to use the Find feature and type in one of those missing
numbers to see if it comes up? Do a Ctrl+F and type in the Invoice
number and click on Find and see if it finds it. If you entered the
wrong date on the form, or selected the wrong AR account or another
account on the invoice screen, then that will affect what comes up
when asking for a specific date range.
You could also go to Reports/Banking/Missing Checks and change the
Account to Accounts Receivable to get a list of invoices. Change the
date range box to All or something like that and see what comes up.
If they aren't there, then someone probably deleted them. Perhaps you
forgot to record them after printing them out.