Why does my reward sometimes not get doubled after I watch an advert?

We're aware that certain adverts aren't correctly doubling rewards and are investigating further why this is happening. In the meantime, some players have reported the following workaround for the Empires and Puzzlers advert:

1. When the advert loads, immediately tap the "Play Free" button. This will open the game's page in your device's app store.
2. Return from the app store back to the game. You should now receive your doubled reward as expected.