How to reproduce:
1. Open user attached project and build it to Android
2. Before running the application, select some music with device Music Player and stop it
3. Launch the built application and observe the Audio Source playing
4. Slide down the notification panel and resume external music playback that was played and stopped with device's Music Player in 1st step, stop it again
5. Return to the application

Expected result: Application resumes to play the Audio Source
Actual result: Application is not playing Audio Source anymore

Reproducible with - 2018.2.0a5, 2018.1.0b11, 2017.3.2f2, 2017.3.0a1, 2017.1.0a1

Note - Losing focus and returning to the application workarounds the issue

DUT (All tests done with default music players):

Reproducible with:
Google Pixel 2 XL*, OS:8.1.0, CPU:arm64-v8a, GPU:Adreno (TM) 540, Build:google/taimen/taimen:8.1.0/OPM1.171019.018/4518263:user/release-keys
Samsung SM N950F*, OS:7.1.1, CPU:arm64-v8a, GPU:Mali-G71, Build:samsung/greatltexx/greatlte:7.1.1/NMF26X/N950FXXU2BQKG:user/release-keys
Google Nexus 5*, OS:6.0.1, CPU:armeabi-v7a, GPU:Adreno (TM) 330, Build:google/hammerhead/hammerhead:6.0.1/M4B30Z/3437181:user/release-keys
Htc HTC Desire 510*, OS:4.4.3, CPU:armeabi-v7a, GPU:Adreno (TM) 306, Build:htc/htc_europe/htc_a11ul:4.4.3/KTU84L/407309.7:user/release-keys

Not reproducible with:
Xiaomi Redmi Note 4*, OS:7.0, CPU:arm64-v8a, GPU:Adreno (TM) 506, Build:xiaomi/mido/mido:7.0/NRD90M/V8.5.4.0.NCFMIED:user/release-keys