Older invoices keep disappearing one day then back the next, it still shows as the correct balance in the customer tab but no invoice number or link to the older invoice

Hi there,

Are the invoices manually created in QuickBooks Online or you're adding transactions from the downloaded bank feeds in QBO? I recommend checking with the Audit Log in your QBO to see any changes made in your account. Here's how:

1. Click on the Settings and click on Audit log.
2. Select the fields to view the period, user, date or events to narrow the results.

Click on View in the History column to view the detailed information.

Checked this link to learn more about audit logs in QuickBooks Online. 

Post again in the Community if you have further concerns. I'm around to help.