Yeah, I see that things started happening since the upgrade, which is why I've been trying to see if anything was added that might be causing the issue.
What I'm seeing however it doesn't look like it. Basically all scripts run through the main ubbthreads.php script. Normally to debug, I'll add something like this:
I'll put that into various spots of the ubbthreads.php script to start. I'll move it down a bit at a time, so when I no longer see that line, then I know it's something above that point that's causing an issue. On your site, I can stick that up right at the top after the opening <?php tag and I never see it, so it's like it won't even begin to execute the php script when it hangs.