Codex App: long project thread scrollbar jumps uncontrollably on Windows

What version of the Codex App are you using (From “About Codex” dialog)?

26.611.61753, released 2026-06-17

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Microsoft Windows NT 10.0.26220.0 x64

What issue are you seeing?

In Codex Desktop on Windows, a long project thread becomes unreadable.

After scrolling for a short distance, the right-side scrollbar thumb starts jumping up and down irregularly. The conversation viewport follows the scrollbar movement and also jumps vertically. This makes it impossible to read earlier messages in the thread.

The issue happens with both:

• Mouse-wheel scrolling
• Dragging the right-side scrollbar

The affected thread is idle, so this does not appear to be caused by active response streaming.

What steps can reproduce the bug?

1. Open Codex Desktop on Windows.
2. Open a local project that has a long Codex conversation thread.
3. Open the long project thread.
4. Try to read earlier conversation content by scrolling.
5. Use either the mouse wheel or drag the right-side scrollbar.
6. After scrolling for some distance, the scrollbar thumb starts jumping up and down irregularly.
7. The conversation page follows the scrollbar and jumps vertically, making the thread unreadable.

What is the expected behavior?

The conversation viewport should remain stable while scrolling.
When the user stops scrolling, the page should stay at the selected position so earlier messages can be read normally.

Additional information

Codex App version:
26.611.61753, released 2026-06-17

Platform:
Microsoft Windows NT 10.0.26220.0 x64

This issue is specific to a long Codex project thread, not a currently running generation. The affected thread is idle.

The issue prevents normal review of prior project analysis and engineering notes.

Possible area to inspect:

• Long-thread virtualization
• Scroll anchoring
• Dynamic message height recalculation
• Markdown/code block rendering height changes
• Windows-specific mouse wheel or scrollbar handling

I cannot use /feedback in the affected thread, so I am reporting this directly on GitHub.