Failed to acquire lock for vm:...:files-sync — blocks agent mid-task

v0
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I’m running into a recurring Failed to acquire lock for vm:{id}:files-sync error in v0.app. This has happened multiple times across different chats/projects over the past few weeks, always in the same pattern:

Pattern:

  • The agent is mid-way through a multi-step task list (usually 3-5 steps), actively editing files.
  • Right before the lock error, there’s typically a heavier file operation — a production build (Built project → Build finished), a large batch of file edits, or several sequential tool calls (typecheck, lint, read files, edit files) without pause.
  • The agent then either:
    • Shows repeated Retried sandbox check / Checked sandbox health attempts that don’t resolve, and the task sits paused for 5-10+ minutes with no progress, or
    • Surfaces the explicit Failed to acquire lock for vm:{id}:files-sync error.

What I’ve tried (partial workarounds):

  • Hard refresh (F5) on the page — sometimes forces reconnection and the sandbox recovers (Reconnected to preview, Switched version appear in logs afterward).
  • Waiting several minutes without sending “continue” — sending “continue” repeatedly while locked seems to make it worse, possibly queuing more conflicting file-sync attempts on the same VM.
  • Breaking large multi-task prompts into single-task prompts — reduces frequency but doesn’t eliminate it, especially when a task involves a build step.

Impact:

  • Lost time waiting for the sandbox to recover.
  • Burned credits on tasks that stall mid-execution (agent keeps “thinking”/retrying while the VM is unresponsive).
  • Not consistently reproducible on demand, which makes it hard to pin down — but frequent enough to disrupt normal multi-step agent workflows.

Ask:
Is this a known issue on the infra/sandbox side? I found a couple of older threads describing similar symptoms (vm:files_sync ... blocking login, Unable to acquire lock at .next/dev/lock), so it doesn’t seem isolated to my account/project. Any guidance on avoiding it, or an ETA on a fix, would be appreciated.

I’m happy to share screenshots/logs of specific occurrences if that helps debug.

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Hi Zetnick258,

This sounds more like the v0 sandbox/file-sync layer getting stuck than a Next.js or React code issue, especially since it tends to happen around builds, large edit batches, or repeated tool calls.

A few things I’d try to narrow it down:

1. Avoid sending “continue” while it is retrying sandbox health checks.
2. Refresh once and wait for the preview/editor to reconnect before giving another prompt.
3. Run only one active v0 chat against the same project at a time, since shared projects can involve the same app/files.
4. Split the workflow into “edit files first” and “run build/typecheck after” instead of asking for both in one long multi-step prompt.

A useful prompt pattern might be:

Make the requested code edits only. Do not run build, lint, or typecheck yet. After all file edits are complete, stop and summarize the changed files. I will ask for the build step separately.

If it still happens, I’d capture one concrete example with the chat URL, approximate timestamp, the exact prompt that triggered it, and the last visible tool/action before files-sync locked. I would avoid posting private project links or secrets publicly, but that small reproducible sequence is probably the most useful signal for someone from Vercel/v0 to investigate.