What it means
A code-split bundle asked for a chunk file that is no longer there. The usual cause is a deploy: a visitor's open tab still runs the old build, which asks for chunk names the new deploy replaced.
webpack calls it ChunkLoadError ("Loading chunk 123 failed"); Vite and native import() say "Failed to fetch dynamically imported module" or "Importing a module script failed". Flaky networks and blocked requests cause a smaller share.
Is it a real bug?
Not in the code that reported it. It is a deploy and caching problem: the fix is to keep the previous build's chunks available for a while after each deploy, and to reload the page once when a chunk fails to load.
A sudden jump right after a release is expected. A steady rate with no deploy means a CDN or caching misconfiguration worth checking.
How to filter it
For any Sentry-compatible browser SDK:
window.addEventListener("vite:preloadError", () => window.location.reload());
Sentry.init({
dsn: "...",
ignoreErrors: ["ChunkLoadError", /^Loading (CSS )?chunk .* failed/, /dynamically imported module/],
});In RealUptime Errors
You do not need the filter above. RealUptime Errors drops this error by default, before it reaches your quota, and counts every drop on the issue list so nothing disappears silently. What we match: An exception of type ChunkLoadError, or a message starting with "Loading chunk ... failed", "Loading CSS chunk ... failed", "Failed to fetch dynamically imported module" or "Importing a module script failed".
To see these errors anyway, turn off the noise filter for a project in Errors settings. It works the same for the RealUptime SDK and for Sentry SDKs pointed at RealUptime.