[Koha] Wiki certificate

[Paul A]

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