Unity ads are broken, at least on IOS. Blank screen for 30 seconds followed by an error message about not being able to connect to the internet and then no reward. The issues with this are (1) it is incorrect as internet connection is available (2) why does it think it needs to connect to the internet? (3) It terminates not only itself, but also any other subsequent ads (from other advertisers) from playing.
I have seen the same problem with Unity ads within other games, but they are only partially broken in those games and still manage to complete. I have used their in-ad reporting feature to let them know the ad is broken but it has been weeks and no change.
I have tried the in-game bug reporting feature within this game (CCFS), but it is somewhat flawed as well, so won't be using that again.