I had the same issue. One of my directories was named C# Practice. It would not recognize any file or directories with it, even if unrelated to .cs files. I believe neovim has some issue with the # character as when I tried to make a file with # in the name it asked me to substitute it. If you have any files or directories with the # or maybe any other special character try removing that character. I simply changed mine to CS Practice and now it works fine.