Thanks for reaching out about your invoices. QuickBooks Online is a great tool able to help you create and send invoices to your customers so they know the services you've provided. I can provide some information about missing invoices.
One possible cause for missing invoices that were entered in your books would be browsing data. These temporary files can accumulate in your browser, system and network and cause errors like information not being shown temporarily in any cloud-based software like QuickBooks Online. Here are some steps to resolve issues caused by browsing data: