[Koha] Wiki certificate

For wiki.koha-community.org, Opera has started giving a SSL Error: Your connection is not private You attempted to reach wiki.koha-community.org, but the server presented an invalid certificate. You cannot proceed because the website operator has requested heightened security for this domain. Firefox (verified by "Let's encrypt") does not stumble. Is this purely an Opera foible? There seems to be a fair amount of "web chatter" about "Let's encrypt" being temperamental on Ubuntu. Thanks -- Paul