Right now, there aren't any problems with opening up the invoice tab to generate a new invoice.
I'd suggest logging into your account QuickBooks Online through a private or incognito window, so you'll have the option again to uncheck the attachment.
This browser window doesn't use the existing cache files, which makes it a good place to find out if there's an issue with the browser.
The first step is accessing QuickBooks Online through the private or incognito window.
Let's use these shortcut keys to get started:
For Mozilla Firefox browser: Ctrl + Shift + P
For Google Chrome browser: Ctrl + Shift + N
For Safari Browser: Command + Shift + N
If it works, return to your regular browser and clear its cache. If not, use other supported web browsers. The current one you're using may have a temporary issue with QuickBooks. Utilizing a new browser allows you to get back to working order.