About 90% of my interaction with Twitter is is clicking a link from HN. When I do so, there's about a 1/3 chance that tweet doesn't load.
I would think that your first visit loaded a resource/set a state somewhere which let's the second visit go through.
Much more likely to be a programming error then a purposeful decision by a PO as the end result is objectively terrible. I cannot imagine anyone getting convinced to register to a webpage that cannot even load. It's not that content is hidden behind a pop-up or anything, it just errors out (at least for me, but I'm not the parent comment author)
Some issues are fucking hard to detect and an initial page load breakage that only happens sometimes (likely a race condition that cannot be replicated in testing) is an example of that