Engraving small font - the bit digs deeper and deeper as the job goes on. 6040z

[magicniner]

As I say my background is a bricklayer or IT professional so terminology is all new to me, but if a motor (1.26nm 178oz on the 6040's I have seen) jams because of shonky engineering presumably it can lose steps

If the coupling can move up or down then it's not holding the shaft tightly enough to reliably transmit all movement and we can reliably derive from this that in the absence of a key device that there is some slip in the drive.
In talking about "lost steps" we are entering the twilight zone of speculation once again, I missed the post where the OP stated that the motor was jamming, still can't find it, the video shows no evidence of jamming BTW ;-)

or is there another term for that.

Yes, the term you seek is Speculation, something which someone in a brief moment of sagacity advised us all against :D

- Nick