Advanced Mining World Not working

We bought Advanced mining world a while back for my son and it has never worked.  He uses it on his kindle Fire.  It is updated so I am not sure what the problem is.   He tries to login and it eventually spits him out of minecraft all together.  Also, it takes a while, sometimes never happens, for him to join world with others playing on a separate device when under the same wifi.  Is there a trick to this?  Is there a way to be refunded or gifted a new world if this can't be fixed?