Play app can't handle more than one function at a time. If you have troops returning then the task you try to do freezes . Play app is of extremely poor quality. Need to refresh it frequently as mail and walkie messages don't come through-just the number. Sick of having to continually refresh for one reason and another.

Have you tried clearing cache? Normally, the game mustn't lag or freeze when your troops are returning to the Base or when doing any other actions in the game. Most likely you'll need to clear cache or reinstall the launcher.