Server Log
If I had to hazard a guess, I'd say this line is the point of no return for connections:
Client Log
Users have no problem connecting to the server and playing until several hours pass, and all of a sudden something happens and users cannot connect to the server anymore until a server restart. If a user is already on the server when whatever error happens, he can continue playing on the server while other users are unable to connect.
I stumbled upon this thread while looking for a solution. I am not suffering from players getting disconnected, but the rest of the symptoms seem to line up. It suggests that the 4.1.9 version of Netty is causing this particular issue. I have no idea how to get forge to use a different version of Netty. Help!
Thanks ahead guys, and great work on forge!
EDIT: After playing for several more hours with no issues and a full server of people, I disconnected to refresh the in-game maps. When trying to rejoin my server I get the error:
failed to connect to server
java.nio.channels.closedchannelexception
Now there is still a full server of people playing, but no new players can join.
Server Log
This time there seems to be no indication of any errors in the server log. I'm very confused.
Client Log
EDIT2: So I did in fact have a player get disconnected when encountering this error:
Server Log
This seems to help confirm that it is indeed the Netty issue highlighted here.