There have been cases when hacked two-factor authentication?
Its possible.
For example if you use the same password across all your accounts including your emails. The hacker could easily have access to your authenticator backup especially those that have cloud backup like Authy.
The best way is to use different random strong passwords for all your important accounts and the activate 2FA for all of them.
This should be done even it's hard to put a different passwords since tendency is we will forgot one of them but it's safer since when one is detected the other will follows. I have different email for my crypto, work and personal . And I triesd to put different password and mostly forgot those I don't use often that's why I add security option in mobile or backup email. 2FA still should be use.