Index: src/wp-includes/class-wp-user-request.php
--- src/wp-includes/class-wp-user-request.php
+++ src/wp-includes/class-wp-user-request.php
@@ -116,6 +116,13 @@
 		$this->confirmed_timestamp = (int) get_post_meta( $post->ID, '_wp_user_request_confirmed_timestamp', true );
 		$this->completed_timestamp = (int) get_post_meta( $post->ID, '_wp_user_request_completed_timestamp', true );
 		$this->request_data        = json_decode( $post->post_content, true );
-		$this->confirm_key         = $post->post_password;
+
+		// See: https://core.trac.wordpress.org/ticket/44940
+		if ( ! empty( $post->post_password ) ) {
+			$this->confirm_key = $post->post_password;
+		} else {
+			// Backwards compatibility for requests lacking a confirm key.
+			$this->confirm_key = wp_generate_user_request_key( $post->ID );
+		}
 	}
 }
Index: src/wp-includes/user.php
--- src/wp-includes/user.php
+++ src/wp-includes/user.php
@@ -4845,7 +4845,7 @@
 			array(
 				'action'      => 'confirmaction',
 				'request_id'  => $request_id,
-				'confirm_key' => wp_generate_user_request_key( $request_id ),
+				'confirm_key' => $request->confirm_key,
 			),
 			wp_login_url()
 		),
@@ -4968,22 +4968,25 @@
  * Returns a confirmation key for a user action and stores the hashed version for future comparison.
  *
  * @since 4.9.6
+ * @since 6.9.0 Request ID optional. See: https://core.trac.wordpress.org/ticket/44940
  *
- * @param int $request_id Request ID.
+ * @param int $request_id Optional. Request ID. Default 0.
  * @return string Confirmation key.
  */
-function wp_generate_user_request_key( $request_id ) {
+function wp_generate_user_request_key( $request_id = 0 ) {
 	// Generate something random for a confirmation key.
 	$key = wp_generate_password( 20, false );
 
-	// Save the key, hashed.
-	wp_update_post(
-		array(
-			'ID'            => $request_id,
-			'post_status'   => 'request-pending',
-			'post_password' => wp_fast_hash( $key ),
-		)
-	);
+	// Maybe save the hashed key to the request, if ID passed.
+	if ( $request_id ) {
+		wp_update_post(
+			array(
+				'ID'            => $request_id,
+				'post_status'   => 'request-pending',
+				'post_password' => wp_fast_hash( $key ),
+			)
+		);
+	}
 
 	return $key;
 }