Folder Under Project Root Remains Hidden Unless I Show All Files

I have a project with the following structure:

C:\DEVELOPMENT\CODINGAUTOMATION\CODINGAUTOMATION.METADATA
│   CodingAutomation.Metadata.csproj
│   README.md
│   
├───bin
...
├───obj
...
├───Reflection
│       ClassReflector.cs
│       
└───Roslyn
        ClassSyntaxTree.cs
        Example1-Program.cs

The Roslyn folder always remains hidden, except if I switch on Show All Files in Explorer, unlike the Reflection folder which behaves normally.

Here is Explorer's normal view:
 

And here is the view when I switch on Show All Files:

I have tried deleting the Roslyn folder, saving the solution, and restarting Rider, but this folder remains hidden when other such project sub-folders, like Reflection are all visible.

here is nothing untoward in the project file, like a <Compile Remove directive or anything:

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>net9.0</TargetFramework>
        <ImplicitUsings>enable</ImplicitUsings>
        <Nullable>enable</Nullable>
    </PropertyGroup>

    <ItemGroup>
      <PackageReference Include="Microsoft.CodeAnalysis" Version="4.13.0" />
      <PackageReference Include="Microsoft.CodeAnalysis.Common" Version="4.13.0" />
    </ItemGroup>

</Project>