We can't help you - we have no access to your file system, and that is probably quite relevant.
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. If you don't know how to use it then a quick Google for "Visual Studio debugger" should give you the info you need.
Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.
I'd also suggest two other things:
1) Remove this line:
Console.WriteLine("Files count: {0}", files.Count().ToString());
That causes the system to enumerate each file - i.e. to search every file and folder in the path in your case - and throw away the result before it gets to actually using the file names!
2) Add logging to your code to record every file it tries to process and every file it does process inside the
switch
. After the run, you can identify all the "missed files" and see if they have anything in common.
Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!