This is from Angelo:
First view the site in various browsers, if each browse the player looks different, then there is a javascript error happening and the browser’s default HTML5 player is loading (Chrome uses rounded corners). The MEJS player is what is built into WordPress, not PowerPress. They can look in the error console of the browser to see what is causing the javascript error. It could be anything, cache server caching the wrong erosion of the MEJS code, jQuery not loading, etc… if the MEJS player cannot load, the default HTML5 player loads, which we believe is your situation.
They should try using the built-in WordPress [audio src=""] shortcode, this should also invoke the MEJS player directly in WordPress. If this works but PowerPress does not then we need the following:
* Version of WordPress
* Version of PowerPress
* URLs where we can see this so we can diagnose the problem: A URL to page with PowerPress and the player not working, and URL to page with [audio\ shortcode and player is working.
If [audio] shortcode does not work, Disable PowerPress, then test the same [audio] shortcode page again. If PowerPress disabled and audio shortcode page now works, there is something going on with caching, they should contact their web host and make sure all caching is cleared with PowerPress enabled before clearing the cache that way you’re starting with a fresh site with everything being correct. Testing with newly open private window also helps prevent caching from mis-diagnosing issues. If PowerPress not enabled and the [audio] shortcode does not work, re-install WordPress.
Make sure you are not using a service such as CloudFlare or Encapsula, these services will cache content without any clear way of clearing it causing these exact situations.