Hello Kim,
Can you please test for a plugin conflict? You could try testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
And since you are using SiteGround, please clear your site cache or at least temporarily 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
Hope this helps.