# BUG: Heartbeat goes into a state of writing billions of error logs

**URL:** <https://discuss.elastic.co/t/bug-heartbeat-goes-into-a-state-of-writing-billions-of-error-logs/386726>\
**Category:** Beats\
**Tags:** heartbeat\
**Created:** [June 5, 2026, 6:10am UTC](https://discuss.elastic.co/t/bug-heartbeat-goes-into-a-state-of-writing-billions-of-error-logs/386726 "2026-06-05T06:10:21Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![up2neck](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/up2neck/32/147633_2.png) [@up2neck](https://discuss.elastic.co/u/up2neck)\
**Post date:** [June 5, 2026, 6:10am UTC](https://discuss.elastic.co/t/bug-heartbeat-goes-into-a-state-of-writing-billions-of-error-logs/386726/1 "2026-06-05T06:10:21Z")

</div>

Hello,

Since version 9.3.1 of our deployment, that now uses 9.4.2 we observe the following behaviour in Heartbeat:

- Heartbeat is deployed with Elastic Agent, that controlled by the ECK operator
- Heartbeat is used for running about 200 synthetics tests, which are configured with Kibana
- After a few days of normal operation, Heartbeat starts writing billions of log entries (apx. 500 entries/second) with the following content:

```json
  {
  "log.level": "warn",
  "component.dataset": "elastic_agent.heartbeat",
  "component.binary": "heartbeat",
  "log.source": "synthetics/browser-default",
  "@timestamp": "2026-06-04T09:36:54.289Z",
  "component.id": "synthetics/browser-default",
  "message": "error decoding json for test json results: unexpected EOF",
  "component.type": "synthetics/browser",
  "log.origin": {
    "file.line": 223,
    "file.name": "synthexec/synthexec.go",
    "function": "github.com/elastic/beats/v7/x-pack/heartbeat/monitors/browser/synthexec.runCmd.func3"
  },
  "ecs.version": "1.6.0",
  "service.name": "heartbeat"
}

```

- CPU consumption becomes twice as much
- Restart of the Elastic Agent's container remediates the issue immediately, without any configuration adjustments

On Github, I found the same issue had reported, but had not been answered: [Heartbeat Browser Monitor can lock up with EOF error · Issue #34560 · elastic/beats · GitHub](https://github.com/elastic/beats/issues/34560)