hyatt claims chase was supposed to notify me.
Notify you of what, that your certs were expiring? They merged your accounts in September, you had ample time to check the expiration date of the nights in your account. The certs expire 12 months from when they're issued, it states that in the application, I'm not sure exactly what you think either chase or hyatt did wrong here.
Regarding your second question, that probably has nothing to do with the merging of your accounts and you should call Hyatt as soon as possible to make sure your account isn't compromised.