Why aren't my conditional compilation symbols working when I dotnet publish my .NET Core 3 project?

I have a project which is targeting .NET Core 3. This project builds and runs fine in both Debug and Release configurations. Both configurations have a Conditional compilation symbol set in Visual Studio of Glue.

The resulting .csproj has the following:

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x86'">
  <DefineConstants>TRACE;GLUE</DefineConstants>
  <OutputPath></OutputPath>
</PropertyGroup>

<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x86'">
  <DefineConstants>TRACE;GLUE</DefineConstants>
</PropertyGroup>

As I mentioned earlier, if I run through Visual Studio, all works fine.

If I publish my app through the command line interface, the resulting app seems to ignore the conditional compilation symbol.

As a test, I added an #if around a section of code which will cause compile errors if the #if is excluded.

#if GLUE
        public MainGlueWindow()
        {
#endif
            mSelf = this;

            ...

If the GLUE conditional compilation symbol is considered, the code should compile fine, but I do get errors when I perform a dotnet publish. The full command I am using is:

dotnet publish GlueFormsCore.csproj -r win-x86 -c Debug

The error suggests the constructor header is missing:

C:\Users\vchel\Documents\GitHub\FlatRedBall\FRBDK\Glue\Glue\MainGlueWindow.cs(95,19): error CS1519: Invalid token '=' in class, record, struct, or interface member declaration [C:\Users\vchel\Documents\GitHub\FlatRedBall\FRBDK\Glue\Glue\GlueFormsCore_tksugttl_wpftmp.csproj]

I should point out that x86 is the only platform in my csproj.

I don't know if the problem is caused by the absence of specifying x86 as the platform, but if so I don't know how to specify that on the dotnet publish command.

Can anyone tell me why the dotnet publish command is not considering the GLUE conditional compilation symbol?

Update 1

I was able to solve the problem by removing the Platform from the csproj PropertyGroup condition, as shown in the following:

  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
    <DefineConstants>TRACE;GLUE</DefineConstants>
    <OutputPath></OutputPath>
  </PropertyGroup>

  <PropertyGroup Condition="'$(Configuration)'=='Release'">
    <DefineConstants>TRACE;GLUE</DefineConstants>
  </PropertyGroup>

While this does confirm that the problem is related to the platform, I'm not sure how to specify the platform when building. This is unfortunately not a final solution for me because other projects rely on the platform and I cannot remove that from all configurations.