[MODEL] Sonnet 5 thinking for 2 days

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Subagent behaved unexpectedly

What You Asked Claude to Do

Rename the PropId into PropertyId (in 90 files just created)

What Claude Actually Did

Fable 5.1 spanwned a Sonnet 5 subagent that kept thinking for 2 days and sometimes returns back with a permission request as if it is executing the task but really slow.

<img width="1218" height="110" alt="Image" src="https://github.com/user-attachments/assets/bf395f18-26df-4ed0-a0c8-b8e7a0419eb8" />

Expected Behavior

main Agent should have checked in with sub agent after 20 min with no progress.

Files Affected

Permission Mode

Accept Edits was OFF (manual approval required)

Can You Reproduce This?

Haven't tried to reproduce

Steps to Reproduce

_No response_

Claude Model

Sonnet

Relevant Conversation

Impact

Low - Minor inconvenience

Claude Code Version

2.1.159

Platform

Anthropic API

Additional Context

The process started working again when switched focus on the subagent once i unlocked the PC.
While checking on it with remote control from Mobile the main agent reported the sub agent was "almost done" every time i asked.

Inspecting the sub agent chat i see no messages from main agent as if Fable 5.1 lied about contacting the sub agent for a status update.