Can you give us more detailed instructions on how to cause/repeat the problem?
This is what I did...
a. Save file. Renamed it to "Dave".
b. Started new Sketch. Renamed it to "Dave".
When into Gallery and I was able to find 2 files name "Dave".
If you are having an issue with 'naming the file', can you keep it as "untitled' and see how much work you can get done before the issue happens again.
David Lau