The video ads can only work when some customer of Vungle had bought a video ad campaign in/for your region. If no ad campaign is available in your region, boosts from video ads are not available.
Furthermore, only a limited number of ads per day is delivered to a single device. Once this limit is exceeded on your device, you can only wait until the next day.
Deleting the VungleSDK folder will help only in the case if one of their ads was broken and killed the local cache of the video ad system. AFAIK, currently there is no such ad in the loop.
FG is just using Vungle (vungle.com) as alternate payment method. When Vungle does not provide payment, because there is no ad to deliver, I’m afraid FG cannot help you.