I've noticed the same and have been looking into it, and I think I can make a few guesses from it. What I've been able to deduce so far is at some point within the year, a change was made that if Comcast is your network provider you'll get a cloudflare javascript captcha challenge irregardless of user agent/cookies/activity/patterns of abuse/page traffic/etc., every single time, but not many (any?) other providers have the same blanket ban as far as I've seen. This extends to all subdomains of srb2.org (main page, forums, screenshots and attachments hosted on the forums, etc), though I couldn't really say why.
There are workarounds for this but it is a little annoying to "bypass", and most of my initial attempts to make it workable are pretty kludgy. I'll try and figure out something.