I am not sure if this is your problem, but I ran into an issue where I would do a G41 and then position the cutter with an X,Y move at the same time (as opposed to X, then Y, and it made Mach3 flip out...
No error code was given, and the DROs kept moving, but my mill jerked to a stop and the stepper motors howled like the table had crashed at the end of travel, but it wasn't even close to a crash.
I changed the X,Y move to a different spot and re-ran the program and the mill did a big loop to get there (It was supposed to be a G01 move, not an arc)
I then changed it to move X then Y after the G41 and it worked correctly. I assumed I was just breaking some rule of G-code programming since I'm new at this.
I see you did an X,Y move immediately after G41 on line N0480.