Hi Jeremy
Thank you for your update.
Yes, we were able to reproduce the reported behavior "Buttons in top banner are not able to click using LeftHeaderItemsSource and RightHeaderItemsSource" in 18.4.0.30v, However it is working fine in 19.1.0.54 and latest versions. So we recommend you to upgrade to our latest version to get the issue fixed. Or please confirm whether your product version is 18.4.0.30v, so that we can check and provide you the patch accordingly.
Regards,
Vijayalakshmi VR