The problem with this feature seems to be that it thinks if the site reissues its certificate it means all passwords there were compromised. Which leads it to mark all old passwords as vulnerable, even if no breaches were actually reported for the site.
The certificate/password link is a guess since on their website they say to change the password starting with date that matches the date of certificate reissuance.
This seems to be related to Hearbleed, also it lists a site that didn't reissue certificate after Heartbleed as vulnerable too, and so for passwords there, seems to be regardless of age.
I am a long-time 1password user and have a lot of old passwords, so for me like 90% of passwords are listed as compromised, which I'm pretty sure is not the case.