Wierd Y axis doubleing width issue

I ran into a wierd issue today that I haven’t seen in my admittedly limited experiance so far. I was printing a quick fit wade’s Extruder, using known good G-code that I have used before. Everything was printing fine until about layer 45 or so, when the printer decided that layer needed to be twice the width that it should have been, but only in the Y axis direction. I’ve seen the Shift print X mm over to one direction issue before, but this one, the software literally told the printer “make the line 40mm” and it said “80mm? Great, sounds like a plan”.

Any ideas what would cause that? I had been printing a fair amount of stuff beforehand, but I’ve printed longer without issue before this. I’m thinking it either has to be a controller glitch, the encoder on the Nema motor, or a computer / USB glitch. The hardware in the computer is solid and displays no USB issues so i’m inclined to rule that out. but what else it could be, I’m at a loss.

Woo, that is strange.

Did it print multiple layers at the double length or just the one? It sounds like the steps per unit calibration (firmware) went haywire; but I’ve never heard of that happening before, especially in the middle of a print. Strange things can happen if you start the print before the g-code is fully loaded, I generally wait until the part shows up in the g-code preview before starting the print.

Are you still seeing the issue?

I don’t know. i killed it about halfway into that layer, and it hasn’t done it again since then. The part was fully loaded, and the gcode was one that I had used before and saved, and reprinting it later worked fine again. The wierdest part was it was just doubled in the Y direction, and it was an almost exact double. it was high enough up that the filiament droop didn’t let me get an exact measurement on it, but either it skipped one way and then the other the exact same amount, or something wierd happened.