We are aware of many reports of the game freezing, usually during a battle but sometimes while on the loading screen. We continue to investigate possible causes for this issue, but have not yet identified the reason for it. We do have a few leads, and would appreciate your help in narrowing the focus.
As of update 1.13 we have determined there is a memory leak, and it can cause freezes. It will happen frequently when playing many consecutive battles over longer periods of time, such as when playing many friendly battles back-to-back. It is advised to close and reopen the game periodically, especially before going into battles with long cooldowns such as Guild Raids, Treasure Beach, and Onslaught.
We sincerely apologize for the inconvenience and negative experience caused by this bug, and it's currently a top priority for us to find and fix.