Load the slideshow block manually if needed.

projects/plugins/jetpack/modules/shortcodes/slideshow.php

@@ -186,7 +186,6 @@ public function shortcode_callback( $attr ) {
 		if (
 			class_exists( 'Jetpack_AMP_Support' )
 			&& Jetpack_AMP_Support::is_amp_request()
-			&& class_exists( 'Automattic\Jetpack\Extensions\Slideshow' )
 		) {
 			// Load the styles and use the rendering method from the Slideshow block.
 			Jetpack_Gutenberg::load_styles_as_required( 'slideshow' );
@@ -199,6 +198,14 @@ class_exists( 'Jetpack_AMP_Support' )
 				$amp_args['autoplay'] = true;
 			}
 
+			/*
+			 * Blocks can be disabled in Jetpack Settings.
+			 * If that's the case, we need to include the slideshow block manually.
+			 */
+			if ( ! class_exists( 'Automattic\Jetpack\Extensions\Slideshow' ) ) {
+				require_once JETPACK__PLUGIN_DIR . 'extensions/blocks/slideshow/slideshow.php';
+			}
+
 			return Slideshow\render_amp( $amp_args );
 		}