Any new firewalls, antivirus updates, etc?
We've changed literally nothing remotely relevant to multiplayer in the latest versions, and other folks are playing multiplayer on the latest beta with no problem, so I don't think it's a bug. You could look in the RuntimeData folder and see if there are any logs there as one idea, though; if it was a bug it should be showing up there.
Anyway, given that nothing that should be of substance to this issue has changed on our end and others aren't having the problem, my guess is that something changed on one of your software, hardware, OS, network, ISP, or similar. Given you're using Hamachi and have a green light, that narrows it down pretty much to software, hardware, or OS.