QuickBooks Online uses browser cache to run smoothly. Sometimes, too much amount of cache stored may cause unexpected behavior of the program. Let's access your account via a private browser to check. Let me guide you how.
CTRL+SHIFT+N for Chrome.
CTRL+SHIFT+P for Mozilla Firefox and Internet Explorer.
After that, go back to the App tab again. If it works fine, you can clear the cache of your regular browser. This helps refresh website and application preferences that might cause an issue with QuickBooks.