Several months ago, you started having a malicious ad problem on this site. There's some particular ad network that claims focus periodically. If you try to type a forum post while one of those ads is displayed, the cursor periodically disappears in the middle of your typing and the letters you type stop taking effect. Having to click back to the text box in the middle of every other sentence is an enormous nuisance, and perilously close to "forum doesn't work" levels of badness.
I was pretty sure that it was due to malicious ads, as if you block ads, the problem vanished. Allow ads again and the problem comes back. I complained about it repeatedly back then, and when the problem didn't get fixed, gave up and just blocked ads on the forum. It's only really a problem for forum usage, not the main page, so I didn't block ads on your main page.
Today, the problem came back, even with ads blocked. I scrolled up and saw that you've found some way to get ads past the ad-blocker. I get that you hate ad blockers, as you need revenue. But you also need for your site to work, and malicious ads impede that.
After a bunch of repeated reloading of the page over the course of typing some lengthy posts, and flipping the ad blocker off and on repeatedly, I may have isolated the problem. On the right sidebar, you have an "MMOs and games to play..." box that highlights some games that have paid for ads here. Right below that, you put a vertical banner ad that is much taller than it is wide. That's the spot where the problematic ads are appearing.
One particular ad network has the vertical banner split into three boxes that are each kind of close to square. You can click an X in the top right of each to make the particular ad disappear, and it asks why you don't want to see that ad. "Because it's breaking the web site" is not one of the options, but it should be. If that type of ad appears, then the forum-breaking behavior of the cursor periodically disappearing happens. If it's a more normal banner ad, then the forum works fine. Clicking to close all three of the sub-ads doesn't fix the problem. It appears that the problem isn't with the particular ads that cover 1/3 of the panel, but the software that delivers the ads.
The malicious ad is kind of stealthy, in that it doesn't load until after well after the rest of the page. It also doesn't load until you've likely scrolled the page way down so that you won't see the ad. That makes it rather useless for advertising purposes. It makes me wonder if it's trying to be a keylogger or something, and the "ads" are just an excuse to be allowed on the page, and that's why it's claiming focus: so that it will pick up your keystrokes. If that's the case, then that's much worse than merely breaking forum functionality.