Let me provide some information about why this is happening. This will guide you on what you'll have to do. Buck Tsai.

Leaving tabs open because you want to go back may sometimes cause tab overload. Every tab that you open is sipping at your system resources and clutters up your browser. Therefore, it leads to slower performance. That is the reason why you're experiencing the issue.

You'll want to press F5 to refresh. Aside from that, this reloads the page or document window. 

Furthermore, you may want to get familiar with some of the main features of QuickBooks Online, I've added this article for more information: Get Started With QuickBooks Online.

Let me know if you have any other concerns with QuickBooks. We're always right here to further assist you.