To reproduce:
1. Open the attached project file
2. Build and Run for Android.
3. Launch application on a device
4. Disconnect device from the computer
5. Press home button to put the application in the background
6. Lock the device and wait for few minutes
7. Open the app from the background and notice that the time drifts between UTC time and time.RealTimeSinceStartup (in bold).

Reproduced with: 2017.1.3p4; 2017.2.3f1; 2017.3.2f1; 2017.4.3.f1; 2018.1.1f1; 2018.2.0b4; 2018.3.0a1

Actual results: UTC time and time.RealTimeSinceStartup are not the same after coming back to the app from sleep
Expected results: UTC time and time.RealTimeSinceStartup are the same after coming back to the app from sleep

Tested on devices:
Google Galaxy Nexus*, OS:4.3, CPU:armeabi-v7a, GPU:PowerVR SGX 540, Build:google/yakju/maguro:4.3/JWR66Y/776638:user/release-keys
Samsung SM G965U1*, OS:8.0.0, CPU:arm64-v8a, GPU:Adreno (TM) 630, Build:samsung/star2qlteue/star2qlteue:8.0.0/R16NW/G965U1UEU1ARB7:user/release-keys

Note: screenshot added bellow