Windows desktop: Thinking Intensity slider snaps back to Instant in regular Chat

Environment

• Windows ChatGPT desktop app
• App version: 26.908.9136.0
• Surface: regular Chat (not Work or Codex)
• Same ChatGPT account works correctly in the mobile app

Steps to reproduce

1. Open a regular Chat conversation in the Windows desktop app.
2. Open the Thinking Intensity control.
3. Select or drag the slider to a middle or higher reasoning level.
4. Release the slider.

Actual behavior

The slider immediately snaps back to Instant. Intermediate and higher reasoning levels cannot be selected. The issue affects both GPT-5.5 and GPT-5.6.

Expected behavior

The selected reasoning level should remain active and be used for the next response.

Troubleshooting already attempted

• Fully quit and reopened the desktop app
• Signed out and signed back in
• Tested a new conversation
• Confirmed the mobile app works with the same account

Additional context

The issue began after updating the Windows desktop app. This appears to be a desktop-client regression rather than an account usage-limit issue.

Start by reproducing the slider behavior in the Windows desktop app version 26.908.9136.0 using the listed regular Chat steps, then compare it with the working mobile behavior. Verify the result for GPT-5.5 and GPT-5.6; the issue is done when intermediate and higher reasoning levels remain selected for the next response.