Internet files may have caused QuickBooks unable to process new invoices. I'd recommend using an incognito or private browser to observe this behavior. In this mode, you can avoid cached data(internet files) while accessing QuickBooks Online.
You can open a supported browser, then use this shortcuts:
Otherwise, use another supported browser to sign in with QBO.
However, if you're using the QuickBooks Online Desktop App, you can go to the Help menu and then select Reset App Data. It will clear the application's data temporarily and reloads new data that makes the app work faster. You can reference this article for the steps that I've shared: QuickBooks App for Windows and Mac: General support.
Let me know how it goes in the comment section below if you need further assistance or share additional details. Anytime I can help. Keep safe!