I’ve had this problem for a long time, I’ve posted on it before without result so I’ll try again.
Using the sequence; Select instance, type ‘M’, drag instance, type Ctrl, input distance, type enter - will not make a copy in the vertical axis. This sequence works with red and green axes, but when specifying blue axis, a duplicate instance will be visibly created (just like in the other axes), but disappears as soon as the command is completed. Oddly, this command works when I do not specify a distance, but drag the copy to an arbitrary distance.
This occurs both on my office PC and my personal Mac laptop with unrelated licenses.
This has been an unresolved annoyance for quite awhile and there are easy workarounds, but my workflow is less efficient and my frustration level gets pretty high.
Has anyone seen this? Any ideas on how to make this simple function work again?