Hi there,
it might be due to a conflicting plugin.
Did you try disabling your plugins to see whether it still occurs?
Best regards
Ok I can confirm it is plugin conflict. But I don’t know which plugin. At first I try deactivate every three. Since there is no change in customizer after four try, I growing impatience. Then I bulk deactivate except security plugin. Funny things is Yoast and Shortcodes ultimate is one of plugin included in bulk deactivation. After that I could change the setting in customizer again.
I will test again later which plugin that cause conflict.