It's still not clear to me what changed between the working and non-working state. A new version of the Arduino IDE? A new version of the AccelStepper library? A new version of the sketch?
Also you didn't answer this question:
pert:
Have you verified that it goes back to the working state when you revert to using that version?
By "that version" I mean the version you were using before updating to the "latest version" (of whatever it is you're talking about).