Hi, here’s what you can try:

First, clear your browser cache, as sometimes it can interfere with saving data. After that, log out and log back in. Make sure you're manually clicking Save as QuickBooks auto-saves, but you may need to confirm the save.

Check if any settings or integrations could be automatically deleting invoices. If the problem persists, try creating a new invoice with a different template to see if that helps.

Hope this helps!