Hello @terrim,
The “siteground-optimizer-assets” folder contains all the minified and combined JS/CSS scripts of your website. The actual scripts, however, are generated by your application. In other words, the issue at hand is not a direct result of the Speed Optimizer plugin, but the “frontend-inspector-2290.min.js” script which is generated by the Yoast SEO plugin.
What I can recommend is to make sure that you have the latest version of the Yoast plugin installed on your website. You may also try to re-install the plugin to ensure that all of the core files are in place and none of them are corrupted.
Since you have mentioned that the issue disappears when you disable the Speed Optimizer, you may try to exclude the affected script from JavaScript combination:
However, it is likely that the underlying issue with the script will remain, so if updating/re-installing the Yoast plugin does not resolve the issue you may consider reaching out to the plugin’s vendors for more information.
Kind Regards,
Preslav Kenanov