So the drop-down menu has completely stopped working for the site, along with layerslider. Please see https://wle-mekong-staging.waterandfood.org/ to see what I mean. The drop-down menu works when editing in cornerstone, but seemingly nowhere else. I was editing the .htaccess file to try and include recommended expires headers, so I’m wondering if that is the problem? But I really can’t see how that would have messed it up and when I try to re-set the .htaccess with a new version, the entire site goes offline.
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.