Hi there. Maybe there's something wrong with the storage on your phone. it could be because it's almost full and since there's no more space it freezes. What kind of android do u have? is the app updated?
Please read the guide linked below for details on the most common issues and how to fix them. Usually a clean install is the first step to take and resolves most of the usual issues; the guide details the steps to take to ensure a full 'clean installation' is achieved - This includes checking redundant folders and a REBOOT!