One Excel returns application/zip while other is OK

[janseris]

returns xlsx.xlsx
returns application zip.xlsx

Project which demonstrates this:
Test project.zip

Or code if you don't wanna open .zip file as .NET MAUI team does:

string folderPath = @"../../../testFiles";
string[] xlsxFiles = Directory.GetFiles(folderPath, "*.xlsx");
foreach (var file in xlsxFiles)
{
    string mime = MimeGuesser.GuessMimeType(file);
    Console.WriteLine($"{Path.GetFileName(file)}: {mime}");
}