How to reproduce:
1. Open the attached project
2. Make sure Development build is enabled
3. Build Sample Scene
4. Build and Run created project via Xcode on device
5. Close Xcode
6. Build project in Unity again with the same title
7. In popup click Replace
Result: Build fails
"IOException: Failed to Copy File / Directory from 'Temp/StagingArea/Trampoline' to '/Users/ieva/Downloads/UI/UICrashtest_ios_TRUNK_Debug': destination path already exists."

Note: Issue didn't reproduce with non development build.
Also didn't reproduce if project wasn't built and run on device.
Only building project, but not deploying doesn't reproduce this issue.

Reproducible: 2018.2.0a5, 2018.2.0b1
Not reproducible: 2018.1.0b13