Let's access your QuickBooks Online (QBO) account via a private or incognito window. This way, we can roll out the possibility of a cache related issue.
Data cache or browsing history that is stored for a while causes uncommon behavior to the browser that can affects the performance of your QBO account. To start with, you can use these
keyboard shortcuts in opening a private or incognito window:
For Google Chrome: Ctrl + Shift + N
For Mozilla Firefox: Ctrl + Shift + P
For Safari: Command + Option + P
If you're able to view your invoice without any issue while using a private window, then we'll have to clear your regular browser's cache. This will make your browser to function efficiently.
However, if the issue persists, I recommend using other browsers. This way, we can check if this a browser-related issue.