Hi there, @ysugie,
I’m not seeing Jetpack Boost being activated to your site at the moment. Could you please reactivate the plugin so we can take a look? Thanks!
I am also seeing some caching and security plugins installed in your site. Could you please temporarily deactivate them to see if the issue persists? If not, it means that there is a conflict with that specific plugin(s).
Let me know what you find out, and we’ll take it from there if necessary. Thanks!