Couple of weeks ago, WhatsApp pulled their app from the Window Phone. The reasons were cited to be technical issues without further elaboration on the issue.
Since then, WhatsApp has been working with Microsoft to fix the issue. Whatever the issue was, the app is now back on the store.
WhatsApp hasn’t given any explanation as to what exactly went wrong. There doesn’t seem to be any other change other than fixes for the mysterious technical issues.
If you’ve been waiting for the app to be back on the store, it’s there now.