Hi, amazing plugin. Thanks for your hard work.
The shortcode [contact-form] is fairly generic and may conflict with other contact form plugins. I noticed that your plugin wasn't showing up on my site, and I figured out it is because it was being preempted by the contact form used by Jetpack, which comes preinstalled by default on many WordPress installations. I ended up getting Clean and Simple by using the editor to change your shortcode to [clean-and-simple-contact-form]. You might want to think about changing the default shortcode as well.