Hello, Graeme,
Thank you for contacting us and for using XStore.
Your site is under maintenance mode, so we can’t check it without access.
Depending on activated options in the cache plugin, settings in Theme Options > Speed optimization can be different.
Currently, we can recommend to activate: Disable Old Browser Support, Disable Emoji, Disable Embeds, Disable Gutenberg Styles, Disable Theme Swiper JS (in case you are using Elementor), also Menu Cache, Ajax Search Results Cache, Static Blocks Cache, Remove Query Strings From Static Resources (when these 4 option is activation you will not see your changes for menu and content immediately, so if you are working on site still, temporary disabled these options).
Avoid an excessive DOM size – read these posts about DOM https://docs.wp-rocket.me/article/1412-avoid-an-excessive-dom-size
https://isotropic.co/avoid-an-excessive-dom-size-on-your-wordpress-website/ Edit your page > element settings and enable Ajaxify for some elements (not tabs and not for first elements on the page) . It should reduce the DOM structure. Also, you may try to reduce the DOM results on the page by reducing the number of sections of the page/elements in the footer or header.
Kind Regards,
8theme team