seems to use a wildcard certificate issued for CN = *.eclipse.org
very likely the same that is used for other services and URLs,
It has been renewed 17/01/17 and is valid until
02/03/2020 with the fingerprints below. My personal guess is
that *some* front end servers serving bugzilla are using the
relatively new certificate, while others are still using a
now expired certificate (which would explain why only some
people are having problems).
Just a blind guess...