How to reproduce:
1. Open the attached project
2. Build and run Main scene on iOS device
3. While project is running click on Landscape Right and then Landscape Left
Result: on the bottom text prints Screen.orientation, notice that Landscape Left prints Landscape Right (it sets Screen.orientation = orientation; to one of the possible orientations)
4. Click on Portrait and then Landscape Left - > Landscape Right
Result: on the bottom text prints Screen.orientation, notice that Landscape Right prints Landscape Left
5. If device supports Portrait Upside Down, click on Portrait, then Portrait Upside Down button on the left
Result: on the bottom text prints Screen.orientation, notice that it is just Portrait

Reproducible: 2019.2.0a4, 2018.30b5, 2018.3.0b1
Not reproducible: 2018.2.9f1

Reproduced on: iPad Pro 10.5" iOS 10.3.3, iPhone X iOS 11.3.1, Phone XS iOS 12.0

Didn't reproduce: iPhone 8Plus iOS 12.0, iPhone 6S iOS 11.0