I normally browse the forum as a guest and only login when I am going to post something. I also run an ad blocker plugin (uBlock Origin) in my browser (Firefox on Linux). And I have my browser security set up so it clears cookies when I quit the browser, so every launch is like a clean start and thus every time I go to the forum, it will look like it's the first time I've visited. (I use a different browser on a different computer for gmail, etc., where I want to stay logged in.) So I suppose any of those could be a factor. I wonder if this could be some side-effect of whatever is being done to block the bot attacks?
It's not a big deal to me since it's so intermittent and transitory. But I thought you might want to know it's happening in case it's a symptom of some bigger issue.