Writing errors are easy to do unless you are a tech writer, last one of those was banned.
"Yes, my 10EE is an I/M machine (with ELSR, for what it's worth). "
Ha, Ha! dude you have shown your set up with a funk aftermarket drive, that is why your ELSR does not function, and why you have threading problems.
I do understand, that most here have not operated a proper functioning drive on a Monarch ee, the drives dynamic brake is critical to the metric thread function.
Keep in mind, the leadscrew on the ee does not kickout with a single tooth clutch like other toolroom lathes, the leadscrew remains engaged. So, the dynamic brake, brings the spindle to a repeatable stop set with the ELSR, When the spindle trips, it will come to a full stop in about a turn at normal threading speeds.
This is a method that is easy on the ee.
Adjust the ELSR so the tool stops at a shoulder at the end of a thread, keeping in mind to add extra if you are running the tool in at an angle.
No relief groove needed, pay attention to the machine, when the ELSR trips the spindle, you withdraw the tool in that last turn, to perfectly fade out the thread every time. Exactly the same threading to the bottom of a blind hole, no relief groove needed!
Working in hydraulics, I have cut a massive amount of screw threads on alot of machines, I cant think of a better set up.
two left hand threads "1 acme" on an arbor for the Delta 12/14 table saw
If your drive does not function like it should, the only alternative is using the thread dial, and rolling the machine back to the mark at the start of the thread, I will explain that, for those that havnt used that method, works well but just takes more time.