I was milling a part and was a good part of the way through it when the mill just shut down in reset mode.  There was nothing I could find that caused it to happen.  So, I gave it an M3 to start the cutter back up.  Now the cutter is spinning.  Then pushed the start from present position button (or whatever it says). The system went back into reset again.  Tried it several times and went into reset, staying at the same command location.  It was on a simple G1X0 command; nothing interesting.  So, I went back to zero and started the program over again.  This time it finished.  Has anyone seen this kind of behavior.  I figured it was some kind of noise problem or something, but it seemed like it some anomaly in the code shutting it down, since it was repeatable.  thanks

It could be caused by electrical noise or it could be caused by mechanical vibration affecting mechanical switches (home, limit, estop, etc.)

Try increasing the Debounce Interval (Config. / General Config.) to 2000 or so and see if this resolves the problem. If it does then, as soon as time permits, you need to investigate the root cause (electrical noise, vibration etc.).

Tweakie.

The point is that the thing is resetting on a particular line of code and it kept repeating there by shutting down right after hitting the resume button.  I lifted the cutter from the workpiece, and it was still stopping in the air on the same line of code.  I was resuming at that same line, and it never moved to the next line, just went into reset.  Then when I started the piece all over again from the start of the code, it went through that same point with no problem.  This behaves like some kind of software issue.
A noise problem would give random results.  This was repeatable until I started everything over again.