Thanks for following up on this thread. I'd be glad to provide some info on your question about the Customize button.
To isolate the issue, I'd like to make sure this isn't a problem with the browser. I recommend clearing the cache, since it can sometimes become full of older data, potentially causing viewing errors in QuickBooks Online. Clearing the cache will allow you to work with a clean slate and resolve errors like this. This article will walk you through the steps depending on which browser you're using: https://quickbooks.intuit.com/community/Getting-Started/How-do-I-clear-my-browser-cache-and-temporary-Internet-files/m-p/186420.
If you're still not seeing the Customize button, you may want to call in to speak with a member of the Payroll Support Team. Agents have the necessary tools, like screen-sharing, to look into your account and determine what's causing this problem. The number to speak with an agent is 1-800-488-7330. The most up-to-date contact information can be found here: https://help.quickbooks.intuit.com/en_US/contact.
Feel free to comment below and let me know how things look after trying this out. I'll be here to help in any way that I can.