Thanks for reaching out in the Community! I'm glad to hear you're taking advantage of the sales tax center in QuickBooks Online to track every sales tax you collect and pay. There isn't any reported issue with the tax drop-down on sales forms, and I want to make sure you can use this tool so that nothing is missing on your invoice.
A good starting point would be to ensure there are no bugs in the software due to a browser issue. To ensure your app or browser is running the program as designed, I recommend following the troubleshooting steps in this article: Clear cache and cookies to fix issues when using QuickBooks Online