Try disabling the sound in the game settings.
We are investigating an issue affecting some Android devices, which causes the game to not work properly in the Kanto and Hoenn regions because of an issue with the sound. This does not affect the Unova and Sinnoh regions.
At the moment we do not have a solution for this other than what we recommended, we apologize for the inconvenience. If a solution is found, we will implement it in future updates.
If you wish, you can try using music mods instead of the default game music. You can search for one you like and download them in our Client Customization forum.