Hi, @Sceat, yes, we are tracking an open issue where sites with custom domains which are subdomains of a root domain are not getting the SSL certificate updated to cover the branch subdomain.
If you see this again, please make a new topic in #admin asking us to correct it. Our support team has a workaround to correct the SSL certificate until the issue is fixed.
When I say "subdomains of a root domain " I mean custom domains like
subdomain.example.com and not
example.com where the branch subdomain will be something similar to
sidy-resident is already updated and I just corrected
sidy-business now. If this need to be done for any other sites, please reply here (or make a new topic in #admin).