The purpose of the UVC is to provide users with a sense of responsiveness. Each time a video is played, its view count goes up, but only up to 300 views.
The purposes of the VVC is to ensure fairness and avoid foul play around view counts. With this in mind, VVC is more strict, employing several measures to prevent click-fraud.
Because the VVC is more strict than the UVC, some videos may be at a point where their UVC is at 300 views, but their VVC is at less than 300 views. In this scenario, once the VVC exceeds 300 views, the displayed view count will resume increasing.