I'm using the same smartphone, but in 4.4 Android version, because until now all I read 5.x Android version is very very bad.
Can try to make a full reset and install again, first connect the game by Google Play Games or Facebook account.
If you are root user, prove to make wipe cache/wipe dalvik cache/wipe factory reset in the recovery options.
If the problem continues, download last 4.4 rom who works for you and install if you can by Odin tools.