Using Atom version 0.114.0-f6400a4 on Windows, I cannot open files via UNC paths (e.g. \\server\fileshare\file.html). The tree view appears as it should, but files appear empty, even though they actually have content. I tried this with HTML and text files.
The files open properly when accessed via a mapped drive letter to the same network location (e.g. U:\file.html where U: is mapped to \\server\fileshare).