Thanks for turning to the Community for support. I want to make sure you're able to view the invoice search bar in QuickBooks Online.
When pages, features, or buttons aren't loading as they should it's typically a browser cache related issue. This can be the result of the cache being too full, but clearing it will get everything back up and running normally. Here's how to get this done in Chrome for example:
At the top right, click More (three vertical dots), then Delete browsing data.
Choose a time range, like Last hour or All time.
Select the types of information you want to remove.