Next.jsの勉強をしていたら以下のエラーが出力されていました。
app-index.js:33 Warning: Extra attributes from the server: data-google-analytics-opt-out
at html
at RootLayout (Server)
at RedirectErrorBoundary (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/redirect-boundary.js:74:9)
at RedirectBoundary (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/redirect-boundary.js:82:11)
at NotFoundErrorBoundary (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/not-found-boundary.js:76:9)
at NotFoundBoundary (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/not-found-boundary.js:84:11)
at DevRootNotFoundBoundary (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/dev-root-not-found-boundary.js:33:11)
at ReactDevOverlay (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/react-dev-overlay/app/ReactDevOverlay.js:87:9)
at HotReload (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/react-dev-overlay/app/hot-reloader-client.js:321:11)
at Router (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/app-router.js:207:11)
at ErrorBoundaryHandler (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/error-boundary.js:113:9)
at ErrorBoundary (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/error-boundary.js:160:11)
at AppRouter (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/components/app-router.js:585:13)
at ServerRoot (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/app-index.js:112:27)
at Root (webpack-internal:///(app-pages-browser)/./node_modules/next/dist/client/app-index.js:117:11)原因
調べていたらChromeの拡張機能の影響を受けていることがわかりました。
解決策
Google Analytics オプトアウト アドオン (by Google) の影響で、この拡張機能はユーザーのブラウザから Google Analytics へのデータ送信を無効化する Chrome 拡張機能です。
自分のアクセスをカウントしたかったので有効にしていたのですがこの拡張機能を無効にしたところ、警告は消えました。