just to clarify - the problems seemed to suddenly start again for no good reason. I am hosting as well on Dragonoid's server, and I looked for an already-open port to host blockland over. I chose 3386 (or whatever it is), the default remote access port, and it worked fine for a week and a half before having trouble with letting people join, even while I was accessing the server and modifying files.
The problem fixed itself, however, and now people can join my server again. The configuration is exactly the same as before. Seems like a weird bug to surface.