Restarts are every 24 hours. However, the 10% I've known to happen before I've left for work in the morning, at which point the server will have been up for only a handful of hours.
The client connects, gets to 10% it's the authentication step which appears to timeout and then disconnect.
I've been on the server, with others, playing fine, when the 10% issue happens to joining players.
If I disconnect and then try to connect again at this point, the same happens to me.
A server (RW) restart is the only thing that fixes it (temporarily).
Not sure if this is relevant, but the server sits in a Virtual Machine, but having said that, the old java version of MR sits on a Virtual Machine on the same hypervisor.
The java server has no problems (runs off same Virtual Switch). This server is sometimes up for a week without a restart, and players connect to, and play on it still without issue.