After running the Rebuild Maven Repository Metadata task, I refreshed to see the status and noticed it said "Unknown running".
This appears to be the default return.
Analysis from Brad Beck states the task may be STARTING and suggestion is to add a state for that.
I feel like this may be a recent change but maybe just unlucky timing on my side. I did not check older NX3 (task (re)added in m4) or NX2 at this time.
I waffled between Bug and Improvement; bug for now but made it trivial.
Debug was off when I noticed this.