Index: src/js/_enqueues/admin/site-health.js
===================================================================
--- src/js/_enqueues/admin/site-health.js	(revision 9c50d3dda56e2265b686ae5aaa0cbdd2a4909322)
+++ src/js/_enqueues/admin/site-health.js	(date 1602096159155)
@@ -66,6 +66,58 @@
 		$( this ).attr( 'aria-expanded', ! goodIssuesWrapper.hasClass( 'hidden' ) );
 	} );
 
+	/**
+	 * Validates the Site Health test result format.
+	 *
+	 * @since 5.6.0
+	 *
+	 * @param {Object} issue
+	 *
+	 * @return {boolean}
+	 */
+	function validateIssueData( issue ) {
+		// Expected minimum format of a valid SiteHealth test response.
+		var minimumExpected = {
+			test: 'string',
+			label: 'string',
+			description: 'string'
+		};
+		var passed = true;
+
+		// If the issue passed is not an object, return a `false` state early.
+		if ( 'object' !== typeof( issue ) ) {
+			return false;
+		}
+
+		// Loop over expected data and match the data types.
+		for ( var key in minimumExpected ) {
+			var value = minimumExpected[ key ];
+
+			if ( 'object' === typeof( value ) ) {
+				for ( var subKey in value ) {
+					var subValue = value[ subKey ];
+
+					if (
+						'undefined' === typeof( issue[ key ] ) ||
+						'undefined' === typeof( issue[ key ][ subKey ] ) ||
+						subValue !== typeof( issue[ key ][ subKey ] )
+					) {
+						passed = false;
+					}
+				}
+			} else {
+				if (
+					'undefined' === typeof( issue[ key ] ) ||
+					value !== typeof( issue[ key ] )
+				) {
+					passed = false;
+				}
+			}
+		}
+
+		return passed;
+	}
+
 	/**
 	 * Appends a new issue to the issue list.
 	 *
@@ -78,7 +130,15 @@
 			issueWrapper = $( '#health-check-issues-' + issue.status ),
 			heading,
 			count;
-		
+
+		/*
+		 * Validate the issue data format before using it.
+		 * If the output is invalid, discard it.
+		 */
+		if ( ! validateIssueData( issue ) ) {
+			return false;
+		}
+
 		SiteHealth.site_status.issues[ issue.status ]++;
 
 		count = SiteHealth.site_status.issues[ issue.status ];
Index: src/wp-admin/site-health.php
===================================================================
--- src/wp-admin/site-health.php	(revision 9c50d3dda56e2265b686ae5aaa0cbdd2a4909322)
+++ src/wp-admin/site-health.php	(date 1602094086032)
@@ -144,7 +144,9 @@
 	<h4 class="health-check-accordion-heading">
 		<button aria-expanded="false" class="health-check-accordion-trigger" aria-controls="health-check-accordion-block-{{ data.test }}" type="button">
 			<span class="title">{{ data.label }}</span>
-			<span class="badge {{ data.badge.color }}">{{ data.badge.label }}</span>
+			<# if ( data.badge ) { #>
+				<span class="badge {{ data.badge.color }}">{{ data.badge.label }}</span>
+			<# } #>
 			<span class="icon"></span>
 		</button>
 	</h4>