I'm seeing an issue were some sourcemaps aren't getting generated in a NextJS application and I'm not sure how to debug it.

We deploy to Vercel and upload sourcemaps to Sentry, the sourcemaps that get generated successfully upload, but we're missing lots of sourcemaps.

Here is an example of the output from Vercel's build logs;

@company/project:build: \~/0f19a506e2f8f51b.js (no sourcemap found)

@company/project:build: - warning: could not determine a source map reference (Could not auto-detect referenced sourcemap for \~/0f19a506e2f8f51b.js)

@company/project:build: \~/0f52eebdadff9e11.js (no sourcemap found)

@company/project:build: - warning: could not determine a source map reference (Could not auto-detect referenced sourcemap for \~/0f52eebdadff9e11.js)

@company/project:build: \~/0f890dcc8f56cc0a.js (no sourcemap found, debug id 75d86540-2e61-5f66-7231-a00fedc9db28)

...

@company/project:build: - warning: could not determine a source map reference (Could not auto-detect referenced sourcemap for \~/turbopack-9b547cc17f45ef74.js)

@company/project:build: \~/turbopack-b1167f93224968d4.js (no sourcemap found, debug id 6d5c4cd8-ed5c-9a8d-6b57-65e5b46ae2ee)

The vast majority of the failed to find sourcemap are at the root level (~/blah.js)

I'm kind of at a loss for the best way to debug these files not having sourcemaps associated with them, any general guideance would be much appreciated, or if specific issues with the below configs, happy to adjust.

Setup

• Monorepo using Turborepo
• NextJS 16.0.10
• Typescript
• Sentry/nextjs 9.40

tsconfig file

{
"extends": "@company/tsconfig/base.json",
"include": \["next-env.d.ts", "**/\*.ts", "**/*.tsx", ".next/types/\*\*/*.ts"\],
"exclude": \["node_modules", ".next/types/validator.ts"\],
"compilerOptions": {
"sourceMap": true,
"outDir": "dist",
"baseUrl": ".",

"paths": { "variables": \["utils/variables.ts"\] },

"moduleResolution": "bundler",
"target": "ES2015",
"lib": \["dom", "dom.iterable", "esnext"\],
"allowJs": true,
"skipLibCheck": true,
"strict": true,
"forceConsistentCasingInFileNames": true,
"noEmit": true,
"incremental": true,
"esModuleInterop": true,
"module": "esnext",
"resolveJsonModule": true,
"isolatedModules": true,
"jsx": "preserve",
"typeRoots": \["../../node_modules/@types", "./types"\],

"plugins": \[
{ "name": "next", "enabled": true },

{
"name": "@styled/typescript-styled-plugin",
"lint": {
"validProperties": \["container-type"\],
"unknownAtRules": "ignore"
}
}\]
}

Sentry Webpack options

const SentryWebpackPluginOptions = {
org: "...",
project: "...",
authToken: process.env.SENTRY_AUTH_TOKEN,
silent: !process.env.CI,
widenClientFileUpload: true,
reactComponentAnnotation: { enabled: true },
tunnelRoute: "/sentry-monitoring",
disableLogger: true,
automaticVercelMonitors: true,
};

Relevant lines from nextConfig

const nextConfig = {
reactCompiler: true,
turbopack: {
root: path.join(\__dirname, "../.."),
debugIds: true,
},

compiler: { styledComponents: true },
serverExternalPackages: \["css-tree"\],

experimental: {
esmExternals: true,
swcPlugins: \[\["superjson-next", { router: "APP" }\]\],
serverActions: { allowedOrigins: \[...\] },
optimizePackageImports: \["@mantine/core", "@mantine/hooks"\],
turbopackFileSystemCacheForDev: true,
},

basePath,
productionBrowserSourceMaps: false,
staticPageGenerationTimeout: 100,
...
}

I've asked the same question in the Next.js community