Random launch failures using iOS 11.2.1 and UE4.18.2

I have created a bare bones arkit app following the instructions in the release notes.

This worked fine and launched without any issues.

I stopped and restarted and now the app cannot be launched, nothing has changed. For some UE4 cannot find a file that was there a few minutes ago???

any ideas?

Here’s part of the log…

LogPlayLevel: … Finished copying to ‘/Library/Caches/engine/content/internationalization/icudt53l/curr/supplementaldata.res’ in 120.01 s
LogPlayLevel: [DD] … Copying ‘/Volumes/Data/work/ios/ar_demos/demo2/Saved/StagedBuilds/IOS/cookeddata/engine/content/internationalization/icudt53l/lang/en.res’ → ‘/Library/Caches/engine/content/internationalization/icudt53l/lang/en.res’ …
LogPlayLevel: Directory (/Library/Caches/engine/content/internationalization/icudt53l/lang) doesn’t exist!
LogPlayLevel: CreateDirectory (/Library/Caches/engine/content/internationalization/icudt53l/lang) failed
LogPlayLevel: Connect: Failed to Connect
LogPlayLevel: [DD] … Failed to transfer a file, extended error is ‘AFCFileRefOpen (/Library/Caches/engine/content/internationalization/icudt53l/lang/en.res) failed with error 12’
LogPlayLevel: [DD]
LogPlayLevel: Exiting.
LogPlayLevel: Took 366.271133s to run mono, ExitCode=1
LogPlayLevel: ERROR: Command failed (Result:1): /Users/Shared/Epic Games/UE_4.18/Engine/Binaries/DotNET/IOS/DeploymentServer.exe Deploy -manifest “/Volumes/Data/work/ios/ar_demos/demo2/Saved/StagedBuilds/IOS/Manifest_DeltaUFSFiles.txt9531cc8649bec0fc7bf19b005b1a62041de63549” -device 9531cc8649bec0fc7bf19b005b1a62041de63549 -additionalcommandline "-SessionId=
8ECBF142594F8970C2296EB8908B0658 -SessionOwner=“lol” -SessionName=“Launch On Device” " -bundle bytecrew.mobile.testing. See logfile for details: ‘DeploymentServer-2017.12.29-16.38.45.txt’
LogPlayLevel: (see /Users/lol/Library/Logs/Unreal Engine/LocalBuildLogs/UAT_Log.txt for full exception trace)
LogPlayLevel: AutomationTool exiting with ExitCode=1 (Error_Unknown)
LogPlayLevel: Completed Launch On Stage: Deploy Task, Time: 449.710019
LogPlayLevel: RunUAT ERROR: AutomationTool was unable to run successfully.
PackagingResults: Error: Launch failed! Unknown Error

Re ran the launch and this time it worked.

This is quite annoying!