What it means
A ResizeObserver callback changed the size of an element it was observing, so the browser would have to run the callbacks again within the same frame. Rather than loop forever, it delivers the remaining notifications in the next frame and fires an error event to say it did.
Chrome and Edge word it "ResizeObserver loop limit exceeded"; newer versions and Firefox say "ResizeObserver loop completed with undelivered notifications". It reaches window.onerror with no stack, which is why every error tracker picks it up.
Is it a real bug?
Almost never. Nothing is lost: the notifications arrive one frame later, and users see nothing. Component libraries that measure themselves (charts, virtualized lists, auto-sizing text areas, many UI kits) trigger it routinely.
It is worth a look only if you also see layout that visibly jumps or never settles, which means two observers are fighting over the same size.
How to filter it
For any Sentry-compatible browser SDK:
Sentry.init({
dsn: "...",
ignoreErrors: [
"ResizeObserver loop limit exceeded",
"ResizeObserver loop completed with undelivered notifications",
],
});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: Any event whose message contains either ResizeObserver loop wording.
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.