So, I'm not sure what is causing this issue.
As of recently, I've been experiencing some pretty bad framerate lockups. It makes me so aggravated to the point where I need to restart the Spiral Knights application but I don't actually want to log off. From what I've observed, this problem mainly occurs if your Knight is presently in a run or in a lockdown game.
To step through the process:
First, I minimize my Spiral Knights application and open up my System Monitor (Linux equivalent of the windows task manager). Or I do sudo killall java in my terminal session.