To reproduce:
1. Open user's attached project
2. Make sure that "bootstrap" scene is opened
3. In the menu bar, click Build -> iOS Player
4. Launch built project on the device
5. Hit "Next Scene" button

Expected result: Scene from the bundle is loaded successfully.
Actual result: Player crashes

Reproduced with: Unity 2017.1.3p1, 2017.2.1f1, 2017.3.1p1, 2018.1.0b7, 2018.2.0a1
Device: iPhone 7+ iOS 11.2.5

Resolution:
This is a known limitation. A user has to hint that a specific component is used in the main app.
- If a component has scripting counterpart just by adding it to link.xml or unused C# script field.
- If it’s only available as Unity component then including an extra semi-empty scene that references all used components works as a hint.