I've been able to host lately (Through UPnP), and all was fine. But as of about 2-4 days ago, nobody can join my server. I was also told that lately other people have had problems with hosting as well.
I do not believe there have been any changes to my computer or otherwise.
When I hosted before, Blockland popped up a window (I'm on a mac), asking if I wanted it to allow incoming connections, I always accepted. It even asked when nobody could join my server, I accepted, and still nobody could join.
But as of now, it doesn't even ask anymore.