Okay, I’ve done that and also updated the plugin. The previous error seems to have disappeared completely and the below error now appears after clearing the Siteground cache when the plugin is activated, and the menu still doesn’t work.
GEThttps://matanuska.co.zw/wp-content/uploads/siteground-optimizer-assets/siteground-optimizer-combined-css-d469a35a2708018485304e3cdb32bacb.css
[HTTP/2 404 Not Found 1694ms]