All ads and videos in the game are provided by 3rd-party companies that rely heavily on the game's cache. If it is full, that may cause errors.
Please clear the game's cache on your device - it's easy:
1. Open Settings >> Apps >> Zombie Castaways
2. And tap the Clear CACHE button (do not confuse with Clear DATA - please do not tap that).
If the problem persists, please, send us a message. If possible, attach screenshots of the videos causing problems, and we will deal with them.