Occasionally builds stop for no known reason

[Michael Feldman]

We are running Bamboo 8.0.4.

Most of the time our builds run fine. But once in a while a build will stop in the middle after about 20 minutes of showing logs on the screen. The logs will be automatically removed. The agent used is also removed. 

The only information is the Error Log at the bottom of the summary tab that says this:

Build <build number> had to be cancelled: it was marked as in progress in DB but no agents were assigned to it.

The status looks like this:

Status Reason for not building is unknown

Sometimes when manually rerunning the build again, the same thing happens for a few times until it is finally successful.

There is no other useful information given.

[Anik Sengupta]

This error in Bamboo indicates the server lost contact with the agent, or the agent died unexpectedly, leaving the build "orphaned" in the database.
The ~20-minute mark often points to a network timeout, resource exhaustion, or the agent process being killed by the OS.

Check Agent Resource Usage: Monitor the agent machine for memory exhaustion (OOM killer) or CPU spikes that cause the agent process to crash.
Investigate Network Stability: Intermittent network drops between the Bamboo server and agent can cause the heartbeat to fail, leading to agent disconnection.
Review Agent Logs: Check the atlassian-bamboo-agent.log on the agent machine directly for errors just before it shuts down.
Check Disk Space: Ensure the agent machine has sufficient disk space, as low space can cause unexpected failures.