Thanks for writing in! Since you are using SiteGround, could you please disable the supercacher in your hosting panel? The SuperCacher is developed by SiteGround exclusively for their customers. It increases the number of hits a site can handle and boosts the website loading speed. The SuperCacher includes 4 different caching options for maximum optimization of your websites. You can access the tool by clicking on the SuperCacher icon in your cPanel.
For more information about this, please check it out here: https://www.siteground.com/tutorials/supercacher/supercacher_intro.htm
For more details how you can improved your site performance, please check this out:
Hope this helps.