I have a similar scenario, receiving a notification on my iPhone that approx 80 of my username/passwords are the subject of a data breach. However many of my passwords on this notification are different. Ie, not the same password across all sites. I often use a similar password but with different letters or numbers at the end.
Some of these notifications even related to my wife's email addresses and passwords, and one was my sons school log-on with different passwords.
So how can it be that all these websites have suffered data breach at the same time??
I can understand the concept of, say, a retailers website getting hacked and suffering a data breach that contains a list of all its customers including my email and password. And I get that as a precaution Apple may notify me about a potential breach for any other websites where I may have the same email & password combination. But why would I be notified of many other passwords being at risk? Is it because they may contain 'part' of the same password? But that still doesn't explain the notifications relating to my wife and sons passwords which are nothing like mine.
Its almost as if Apples whole key chain password app in my iPhone has been compromised and its spat out all the ones that don't contain a 18 key encryption.
I'm slowly working through them all again and changing them.
Thanks