Steps to reproduce:
1. Download "Sandbox.zip" attached by the user
2. Connect an iOS/Android device with Unity Remote 5 opened in it
3. If your computer has a built-in webcam, change these lines in WebcamTextureHolder.cs:
26: yield return new WaitUntil (() => WebCamTexture.devices.Length > 1);
28: webCamTexture = new WebCamTexture(WebCamTexture.devices [1].name, 640, 480);
4. Enter play mode
5. Click the button in the scene

Result: Fatal error "CheckDisalowAllocation" happens and Unity freezes.
Expected result: no freeze/successful scene transition
Reproduced on: 5.6.1p3, 2017.1.0b9, 2017.2.0a3
Did not reproduce on: 5.5.4p1 (getting this error in Console instead: "Assertion failed on expression: 'state.object->ShouldIgnoreInGarbageDependencyTracking() == !addToNeedsProcessing'")

Devices used: LG Nexus 5X (Android 7.1.2), iPhone 5 (iOS 9.3.5)
Tested on: MacBook Pro (Retina, 15-inch, Mid 2015)