Yeah, based on the video, it looks like the M relay doesn't fire for a bit and then when it does, the 10k stepper stops stepping.
The circuit to the M relay is usually completed through a switch on the back side of the 10k stepper that closes as the drive arm (i.e., the big, metal arm towards the bottom back of the stepper that pivots to cause the stepper to step up) moves when the 10k stepper coil engages. I've had a few cases in which a poorly gapped or dirty switch prevented the M relay from firing consistently and resulted in the situation you have.
You should be able to peer behind the bottom lower left of the 10k stepper to inspect this switch (or just loosen the two bottom support screws and remove the top one so that you can remove the entire stepper to check out its back side). If I remember right, there's one NC switch that opens (and opens the circuit that keeps the N relay engaged) and one NO switch that closes when the drive arm moves (to complete the circuit to the M relay--this is the one that might be causing your problems).