This looks like the very poor idea of giving scary feeling to the many new users. They never bother to inform all the investors about this mistake from their end. It looks like they have taken granted to every investor. No official notification received about this until yesterday I faced this issue and chat with support and spent more than an hour.
Just re-generate the same adresses you had by clicking "generate". They will show again. That's all.
There are plenty of other wallets that required to re-open a file, a database or import priv key after a big update.
It is easier here.
It will be automatic later, I think.