Run this code

public static void Main()
{
   for (int i = 0; i < 10000; i++)
   {
      new StackTrace(true).GetFrames();
   }
}

on Windows10 with .net 4.7.1 and it will take 5 seconds to complete.
Run this code on the same system without 4.7.1 and it will take 200ms

There is performance degradation in System.Diagnostrics.StackFrameHelper.InitializeSourceInfo

Looks like caching is broken and pdb files are loaded every time