Cowork on Windows: KB5124008 killed the sandbox shell for me (Plan9 mount fails). Anyone else?

A user reported that the Windows update KB5124008 (build 26200.9445), installed on September 9th, broke the Cowork sandbox on their laptop, specifically causing Plan9 mount failures. Uninstalling the update resolved the issue. The user is seeking to know if others have experienced this problem and if there's a way to retain the KB while still having the mount function correctly.

This report is among the first to identify Windows update KB5124008 as the cause of Cowork sandbox Plan9 mount failures, unlike general reports of update issues.