There are a few reasons why QuickBooks Online behaves unexpectedly. It could be a browser-related issue that can be resolved by doing a few basic troubleshooting steps.
First off, let's use an incognito or a private browser to confirm the issue. Open any browser of your choice, then follow these shortcut keys to use an incognito window:
Chrome simply press Ctrl + Shift + N.
Mozilla Firefox and Internet Explorer, press Ctrl + Shift + P.
Safari, press Command + Shift + N. Make sure you're using the latest version.
Check your customer's list and see if it's now listed alphabetically, then follow the steps toclear your browsing data if it does. This will allow QuickBooks to load as a fresh page to remove any error messages or glitches that may be standing in the way of certain features.