To reproduce:
1. Create a new project
2. Build it for iOS platform
3. Run on the device
4. Turn device to change screen orientation
5. Inspect the Xcode console

Expected result: No error should appear while changing screen's orientation
Actual result:
2018-02-27 16:32:20.264264+0200 ProductName[760:1340236] [App] if we're in the real pre-commit handler we can't actually add any new fences due to CA restriction
^ error appears when the orientation is changed.

Reproduced with: Unity 2017.1.3p1, 2017.2.1p4, 2017.3.1p2, 2018.1.0b9, 2018.2.0a2
Device: iPhone 7+ iOS 11.3

To disable these warnings:
Click on your active scheme name right next to the Stop button
Click on Edit Scheme...
in Run (Debug) select the Arguments tab
in Environment Variables click +
add variable: OS_ACTIVITY_MODE = disable

Won't fix since it's the issue on an iOS side: https://forums.developer.apple.com/thread/52366