This usually happens when editing other C# script files. Occasionally I'll notice that a Pinned Folder window has a valid directory path, but isn't listing any of the files (there's also no errors in the log, which might be because there's too many empty try/catches). Some other times, I've found that same window to have lost even its folder path (in which case it will just display Folder as the window title).
Find out why this is happening, and see if it's fixable.