I have experienced that sometimes too and from my experience I think it mostly happens when the forum traffic is way high. But sometimes the strength of our internet connection can also be a contributing factor.
This is beyond internet issue as it's happening to majority of the users here. So are you saying that most of us experiencing this issue are using the same network? I was also stuck with this issue of human verification while trying to access the forum and on my own case, even after I've verified and the rest and say I want to reply to a post, I get hit with the same stuff and it's mildly irritating to be honest.
Dunno why these things keep occuring. If it's not gateway timeout issue, it will be something else. Is there a way to solve this problem or are we experiencing this anomaly because the forum is undergoing some form of fixing?