GitHub Actions "lost communication with the server" - Runner Dropped

The control plane stopped hearing from the runner mid-job and marked the work failed. The runner crashed, lost its network, or was reclaimed - an infrastructure event, not a problem with your code.

What this error means

A job fails with The runner has received a shutdown signal or lost communication with the server, often abruptly with no application error. The runner went away while the job was still running. Re-running on a healthy runner succeeds.

CI log

The self-hosted runner: build-runner-7 lost communication with the server.
Verify the machine is running and has a healthy network connection.

Common causes

The runner host crashed or was reclaimed

An OOM at the host level, a kernel panic, or a spot/preemptible reclaim takes the runner offline mid-job, so the control plane loses its heartbeat.

Network partition between runner and control plane

A transient network drop between the runner and the orchestrator stops the heartbeats. The control plane cannot tell a partition from a dead host, so it fails the job.

How to fix it

Retry the job

Re-run the workflow - a lost runner is transient and a fresh runner usually completes the job.
If it recurs on the same host, check that host’s memory, disk, and network health.
For self-hosted fleets, ensure runners auto-recover and rejoin after a drop.

Stabilize the runner host

When this repeats, look for host-level resource exhaustion or flaky networking.

Terminal

dmesg -T | tail -50          # kernel panics / OOM at host level
df -h && free -m             # disk/memory pressure on the host

How to prevent it

Run on stable capacity for jobs that cannot tolerate interruption.
Monitor self-hosted runner host health (memory, disk, network).
Make jobs idempotent so a lost-runner retry is safe.