Same problem happened last night.
Thanks to all for the help.
Yes, I'm using TCP.
Ray has looked at my logs and thinks it is a timing issue. My data goes from mount via Cat6 to LAN switch via fiber to another LAN switch and then via Cat6 to the computer. I will advance the timeout setting from 100ms to as much as 500ms, a bit over time to fine the sweet spot. I'll also set up the backup COM port using a USB connection. I can also take the second switch out of the loop if needed.
I'm using the brick power supply that came with the mount. I also have the Powerwerx power supply, for now attached to my 1100. If the problem persists I'll use that power supply on the Mach2 and see if that solves it.
Once again, my thanks to this great community for their support and good counsel.