UCCNC, you'll need a compatible motion controller (UC300eth-5lpt is my preference), but that just means getting rid of your ESS. Not that the ESS is the problem. Cost to convert isn't all that much, but UCCNC has been dead reliable for me, but you can also run Mach 3, and Mach 4 with the UC300eth-5lpt. So that's nice.
All of that said, it sounds like you might have issues bigger than just Mach 4. Programs shouldn't disappear. Can you find Mach 4 on your C drive after it disappears?