1. What happened
UWP App fails to deploy at first attempt when using "Generate C# Projects"

2. How we can reproduce it using the example you attached

1. Create new project
2. Build to empty folder with selected "Generate C# projects" option
3. Try to deploy
4. Fails with following output:

3> Copying unprocessed assemblies...
3>F:\Work\Metro\_BUILD\New Unity Project 5\New Unity Project 5.csproj(235,5): warning MSB3026: Could not copy "F:\Work\Projects\New Unity Project 5\bin\UWP\x86\Debug\Unprocessed\Assembly-CSharp.dll" to "F:\Work\Projects\New Unity Project 5\bin\UWP\x86\Debug\Assembly-CSharp.dll". Beginning retry 1 in 1000ms. The requested operation cannot be performed on a file with a user-mapped section open.
[........]

If you hit run once again, everything works fine.