Apply suggestions from code review

Co-authored-by: Francesco Novy <francesco.novy@sentry.io>

Author: s1gr1d

packages/nextjs/src/common/wrapRouteHandlerWithSentry.ts

@@ -20,7 +20,7 @@ import { flushQueue } from './utils/responseEnd';
 import { withIsolationScopeOrReuseFromRootSpan } from './utils/withIsolationScopeOrReuseFromRootSpan';
 
 /** As our own HTTP integration is disabled (src/server/index.ts) the rootSpan comes from Next.js.
- * In case there is not root span, we start a new span. */
+ * In case there is no root span, we start a new span. */
 function startOrUpdateSpan(spanName: string, cb: (rootSpan: Span) => Promise<Response>): Promise<Response> {
   const activeSpan = getActiveSpan();
   const rootSpan = activeSpan && getRootSpan(activeSpan);

packages/nextjs/src/server/requestIsolationScopeIntegration.ts

@@ -4,6 +4,7 @@ import {
   getCapturedScopesOnSpan,
   getCurrentScope,
   getIsolationScope,
+  getRootSpan,
   setCapturedScopesOnSpan,
   spanToJSON,
 } from '@sentry/core';
@@ -25,7 +26,7 @@ export const requestIsolationScopeIntegration = defineIntegration(() => {
         const data = spanJson.data || {};
 
         // The following check is a heuristic to determine whether the started span is a span that tracks an incoming HTTP request
-        if ((getSpanKind(span) === SpanKind.SERVER && data['http.method']) || data['next.route']) {
+        if ((getSpanKind(span) === SpanKind.SERVER && data['http.method']) || (span === getRootSpan(span) && data['next.route'])) {
           const scopes = getCapturedScopesOnSpan(span);
 
           // Update the isolation scope, isolate this request