C# project Folders not showing in files explorer view - multi-root workspace

## The Issue
Folders in a multi-root workspace does not always remain visible in the files explorer. This may have something to do with one of the folders being a C# project, as this bug does not occur with multi-root workspaces if they consist only of folders with code in other languages.
Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.137.0 (AMD64)
- OS Version: Windows 11 25H2 workstation, build 26200.9445 (AMD64)

Steps to Reproduce:

1. Open a multi-root workspace with one of the folders containing one or more C#/dotnet projects. (tested with a workspace that had a folder of Lua scripts and another with ~5 C# projects, all part of the same solution).
2. Observe that the folder shows up in the files explorer.
3. Expand the folder, or other folders in the workspace.
4. Observe that the folder disappears from files explorer.

## Additional note
Initially, it was assumed that this was an accessibility regression, as the NVDA screen reader is used in conjunction with VSCode. Further testing shows that this might not be the case, as a scanned screenshot with AI and sighted assistance agree that the folder has indeed vanished from the files explorer. It still exists in the workspace as the C# project details are still visible, but trying to edit source code from that view is tedious compared to the files explorer.