To reproduce:
1. Open users attached project "New Unity ProjectDELETE.zip"
2. Open "SampleScene.unity" scene
3. Enter Play mode
4. Observe console for Debug error "Active world exists"
5. Build for iOS
6. Deploy the Xcode project to an iOS device
7. Observe Xcode console as "Active world is null"

Expected result: when built to iOS device World.Active is not null
Actual result: when built to iOS device World.Active is null

Reproduced on:
2018.2.0a9 2018.2.10f1 2018.3.0b3 2019.1.0a2

Did not reproduce on:
2018.1.9f2

Device reproduced on:
iPhone 7 Plus iOS 11.1.1

Notes:
Works fine on a Standalone build with Windows 10 and MacOS.
When building to Android getting burst package errors.
On 2018.2.0a8 and earlier can only download Entities 0.0.12-preview.15, which gives lots of packages errors.