Mention that attribute 'saslMechanisms' attribute in listener entity with value 'ANONYMOUS' in a combination with attribute 'authenticatePeer' with value set to 'yes'
is a broken configuration

What it makes is that when you say authenticatePeer: yes, it removes ANONYMOUS from the list of supported sasl mechanisms.

example of such listener

listener {
    name: secured_default_listener
    host: 0.0.0.0
    port: amqp
    authenticatePeer: yes
    saslMechanisms: ANONYMOUS
    role: normal
    sslProfile: my_profile
}