I think there is a problem with the “back” button on Android. I’m talking about the device button, not the game’s one. I play on a HTC One and I have a “soft” button that has the “back” feature.
This morning, while doing my daily realm, I accidentally pressed on this button. The game has exited and I think it has saved my game. But when I loaded the game again, I was back on the castle and can’t resume or start again my daily realm. My luck is that my streak is not broken though.
I think you should deactivate this button, or make it open the menu or anything but not exiting the game.