Hey there! Could you send a link to the affected page? I tried this on my test site, and it works whether I use /shortcode to pull up a shortcode block or simply paste that code on its own line.
Also, just to be clear, is the site hosted here? If it isn’t, you’ll want to be sure you’ve got Jetpack with the extra shortcodes module enabled, and you’ll want to be sure other plugins aren’t conflicting. Then if you need more help, you’d want to use the Jetpack forums or reach out directly to their support: https://jetpack.com/contact-support/