Unfortunately, this is according to Elsa at Storm8:
Advertisements allow us to let everyone download and play the app for free and to continue supporting the game with new content.
I get that as a business they need to make money but I think it's really bad Storm8 has gone down this particular route. This will run off many players, especially when it keeps glitching and crashing the game. I'm guessing it was a recent app update that added these new popup ads. You are not alone in being put off by it, many others are as well.
Good luck with it, Curlyee