How to reproduce:
1. Open the attached project
2. Open Services window
3. Set organization and enable Ads
4. Build and run on Android (Nvidia Tegra) device
5. Click "showAds" button, you'll see a video ads from Vungle
6. Close the ads view after the video finished, then you'll see a reward popup.
7. Repeat step 2 and step 3 multiple times(~10), the app crashes before the reward popup. (if you can't get the crash, try to restart the app)

Reproducible: 5.5.0b9, 5.5.1p4, 5.6.0b9
Not reproducible: 5.4.4p3

DUT(reproducible):
Google Pixel C [C1502W], NVIDIA Tegra, OS 6.0.1
Goole Nexus 7 [grouper], GeForce, nVidia Tegra, OS 5.1

DUT (not reproducible):
LG G5 [LG-H850], Qualcomm Snapdragon 820, Adreno 530, OS 6.0.1;
Nexus 5x[LG Nexus 5X], Qualcomm Snapdragon 808, Adreno 418, OS 6.0

Not reproducible (got fixed with another bug): 2017.1.0b7, 2017.2.0a1