XCode 6.1.1 (Simulator iPhone 5s iOS 7.1) and Appium 1.3.4 Problem with executing tests

I am using XCode 6.1.1 (Simulator iPhone 5s iOS 7.1/8.1) and Appium 1.3.4. When executing UI iOS tests more than 90% are getting skipped with error code 146.
Full error: “A new session could not be created. (Original error: Command failed: An error was encountered processing the command (code=146): Unable to erase contents and settings in current state: Creating // stderr: An error was encountered processing the command (code=146): Unable to erase contents and settings in current state: Creating )”
To get tests being executed correct I have to reinstall iOS simulator, clear up the Library/Developer/CoreSimulator/Devices folder. Just after that it will run tests fine, but also not for sure.
What could be the reason for such behavior?