Looking at the page source it seems two files are not being enqueued as they should. They are:
As you see one is a core WordPress js file and they other is the Form js file. My guess is that something, another plugin perhaps, is de-enqueuing the required core WordPress
jquery.form.min.js file which will cause the Form js file not to be enqueued.
Or… something else is really “funky”. I looked at the page using the Slim Plus template and I see its js file is not being enqueued either. The above issue wouldn’t affect the template.
Do you have some sort of caching being used, plugin, apc, memcached, Cloudflare, ect…?
If you do, try flushing them. Not sure that would be the cause though since the CSS files are being enqueued.
Can you please try adding SCRIPT_DEBUG to your
wp_config.php file, temporarily? It may help resolve whats happening.