I’m not familiar with the particular machine, but it’s possible that when the 10k stepper steps from 90k to 0k during the startup sequence, it is not engaging the 100k stepper so that it steps up from its negative 1 position to its zero position. During the startup sequence, usually the circuit to the 10k stepper goes through a switch on the motor and a connection that is made when the 100k stepper is at its negative 1 position. Good luck!

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).

Good luck!