Ah, here you go:
* 20 certificates per registered domain per week (up from 5).
* Added an exception to this limit for renewing certificates (issuing a new certificate with same names as a previous one).
* Added a new limit on issuing certificates with the exact same set of names: 5 certificates per FQDN set per week.
Note that if you have a domain with more than 20
subdomains, the exception we added for renewing certificates allows you
to gradually increase the number of certificates you can issue over the
course of multiple weeks.
The limits don’t apply to renewals, so I really think it’s an issue with the Plesk plugin! Since creating certs for domains with the exact same FQDN is limited to five per week, I’m guessing you hit that limit. I’ll hazard a guess that you’re set to renew daily? And it took about 5 days to get this error?