Certificates
Every certificate change the probe has observed, everything due to expire in the next 90 days, and when each host is expected to rotate. Expiry and renewal are different questions: a certificate expiring in 40 days may be due to renew in 10. Cadence is measured from your own rotation history, so a host needs at least two recorded renewals before an interval can be shown.
When each host is expected to rotate, which is not the same as when it expires. A Let's Encrypt certificate expiring in 40 days normally renews in about 10. Predictions marked measured come from your own renewal history; assumed ones come from typical behaviour for the issuing CA.