[Possible Fix] java.net.SocketException: Socket closed

Hello,
I had issues with bukkit. After 10-60 mins all players get disconnected from my server. This is the error in the console

18:22:14 [SEVERE] java.net.SocketException: Socket closed
18:22:14 [SEVERE] at java.net.SocketOutputStream.socketWrite(Unknown Source)
18:22:14 [SEVERE] at java.net.SocketOutputStream.write(Unknown Source)
18:22:14 [SEVERE] at java.io.BufferedOutputStream.flushBuffer(Unknown Source)
18:22:14 [SEVERE] at java.io.BufferedOutputStream.flush(Unknown Source)
18:22:14 [SEVERE] at java.io.DataOutputStream.flush(Unknown Source)
18:22:14 [SEVERE] at net.minecraft.server.NetworkWriterThread.run(SourceFile:116)

I have tried to give my server more RAM: Same error and a chunk error
Vanilla: Same error
Bukkit with no plugins: Same error

But this worked for me:
Enable Keep Alive in you router settings (see image)

I think that my router disconnects me for 1 minute and then the server chrashes.
View attachment 9140