Developer Post-Mortem on Four Incidents While Running Multiple Claude Code Instances Concurrently

On 2026-11-05, DEV Community's AI channel published a write-up titled "Multi-Instance Concurrency: Four Incidents Running Claude Code". The author is a developer who runs several Claude Code sessions side by side, one for a work plugin and others for a small information site, data collection, and video. He recorded his experience in a Korean ebook, and the article excerpts four of those incidents. The first: two sessions edited the same file, and a change the author had not approved ended up deployed. Since then, each session has had a defined scope and owns specific files that nothing else touches. The second: a scheduled job failed quietly, with no alert raised when it hit a failure. Based on these cases, the author advises that each session have a clearly defined file-operation scope, and that unapproved changes never be deployed directly. He notes these lessons can help developers avoid file-conflict risks when working with multiple concurrent AI agents. So far this is the only published account of the matter, and the timeline rests on this single write-up.