Where to start, where to finish?
1) When registering for the website, an insecure call is made to gstatic.com; this should be a call over https.
2) The site certificate doesn't contain the Subject Alternative Name (SAN) of forums.buffalotech.com, thus spawning browser warnings for invalid certificate as the certificate delivered is for buffalotech.com, no wildcard.
3) There is a bad redirect or implied redirect on the SSL/TLS site that rewrites
https://forums.buffalotech.com to
https://www.forums.buffalotech.com, which then fails to connect.
In short, https is unavailable for the forum for some browser users.