WACK fails when in Player Settings "Product Name" has a space in it's title. Reproducible on Universal 10 IL2CPP platform.
With .NET backend WACK passes.

Attached validation results file.

Reproducible on 5.3.5f1, 5.4.0b18 versions.

Repro steps:
1. Create an empty project or open attached project "winUWPbug.zip";
2. In Player Settings write "Product Name" title with a space in it (example: "Space Between").
3. Set platform to WSA Universal 10 with IL2CPP backend and build it.
4. Run WACK on created project.

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Workaround: use .NET backend or don't leave spaces in "Product Name".