Do you only have the one program in memory? IOW, could you make some more room by removing some programs to see if that makes a difference?
Other than that, I'm not sure. Does cutter comp happen to be active in the area where the hang occurs? I've had the odd instance where the machine would stop moving during a compensated path, but it is rare.
What version is your Haas software? That might help someone diagnose the problem.