Failing on Android Mobile or Linux, working on desktop

• Theme (include link): Astra Theme (https://wpastra.com/)
• Post type: Standard
• Post Template used: Site Origin
• Details on how image is added to post: Normal Gallery Widget
• Other plugins installed: Astra Pro, Astra Widgets, Customizer Export/Import EmedPress, Official Statcounter, Page Builder by SiteOrigin, Portfolio, Query Monitor, reCatcha by BestWebSoft, Simple Lightbox, SiteGround Optimizer, SiteGround Security, SiteOrigin Widgets Bundle, Smart Slider 3, Smash Balloon Instagram Feed, Smush Pro, SyntaxHighlighter Evolved, TranslatePress – Business, TranslatePress – Multilingual, Ultimate Member, Ultimate Member – reCAPTCHA, Updraft Plus, Backup\Restore, WP Recipe Maker, WPMU DEV Dashboard
• Screenshot of SLB’s settings page: All settings default, expect Dark Theme.

Hi, I am seeing the same behavior in all browsers at the link provided: SLB is being prevented from fully loading.

This is generally caused by a conflict or error in another plugin or the active theme.

Another user recently found that SiteGround Optimizer modified the order code was run on their page, causing issues with plugins including SLB. You may want to check for this on your site by temporarily deactivating SiteGround Optimizer and checking to see if SLB is able to fully load.

If you are still experiencing an issue, please follow these instructions for identifying plugin/theme conflicts. Please provide the name and link to the conflicting plugin(s), and I will see if anything can be done from SLB’s end.

Please also remember to clear all caches (site and browser caches) and fully refresh the page whenever making changes to ensure that you are not loading stale data.

That was the culprit. Simple Lightbox did not appear in the JS exclude list for SG Optimizer, but did in CSS exclude lists. I excluded the CSS for Simple Lightbox as a first step. I discovered turning off the “Defer Render-blocking JavaScript” feature in the frontend optimization, and adding the following snippet to remove the lightbox from combination and minification fixed the issue – and did not slow my site down noticeably according to GTMetrix.

add_filter( 'sgo_js_minify_exclude', 'js_minify_exclude');
function js_minify_exclude( $exclude_list ) {
    $exclude_list[] = 'slb_core';
    $exclude_list[] = 'slb_view';
	$exclude_list[] = 'slb-asset-slb_baseline-base';
	$exclude_list[] = 'slb-asset-slb_default-base';
	$exclude_list[] = 'slb-asset-item-base';
	$exclude_list[] = 'slb-asset-ui-base';
	$exclude_list[] = 'slb-asset-image-base';

    return $exclude_list;
}

I found this script instruction at https://www.ads-software.com/support/topic/how-to-use-sg-optimizers-filters-procedure/.

Glad to hear your issue was resolved ??