This also started the same time that my Arma 3 launcher stopped working, as seen in ticket 0020203, which is still waiting to be resolved ((at this time) I'm curious as to if there's a relationship between the problems.)
I recently moved the location of my Arma 3 profile saves, the launcher not working started after this, but I did not check multiplayer, but surely changing profile location shouldn't cause the multiplayer to just freeze.
Latest .rpt uploaded.
(Later Edit - Dev build fixes my Launcher problem so that's ok, but MP hosting still doesn't work.)