I am using version 26.313.41514 on Windows 11. Since today (March 18, 2026), all threads have disappeared from the sidebar. The issue affects threads in two different projects.
The PC was restarted between March 17 and March 18, but no updates were installed during that time.
I asked Codex to recover the sessions, and they are still present in the directory .codex/session/yyyy/mm/dd. Codex attempted a recovery, but after restarting the program, the restored threads disappeared again.
I recently saw something similar while demoing the app to a friend. After a restart, the conversations were gone.
Other than my experience that some issues sometimes disappear after an update rolls out, I can only speculate about what is causing this.
Are you perhaps using the WSL agent environment? That can be changed in the general settings. Another possibility is that the ChatGPT account is not properly connected at the moment.