Kind people in the comments pushed me into different ideas and I was able to find and fix the issue.

The issue was the path in this method below, System32 was missing.

private bool IsWinPE()
{
    string windowsDir = "X:\\Windows\\System32";
    return File.Exists(Path.Combine(windowsDir, "winpeshl.ini")) ||
           File.Exists(Path.Combine(windowsDir, "startnet.cmd"));
}

It was my mistake, but this error misguided me and I was looking completely different directions. So if someone will have same problem, this answer may be the solution. Thanks