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Hi haiayu,
Thanks for your information above. Can you please try to enable WP_DEBUG? to check if there’s something wrong on your site. Also, please try to disable WP Super Cache at this moment. Then please try again to install the required plugins for JNews such as JNews Essential, Vafpress Format UI and WPBakery Page Builder plugin.
About enabling WP_DEBUG, you can find the instructions here http://support.jegtheme.com/documentation/system-status/ then jump into WP Debug section. Let us know if you need something else.
Thank you