Notification stating "Rotation is already locked for all concentric mates" (pictured below) when attempting to lock a concentric mate.
However, the bolt still spins and the model is listed as undefined, so this is quite the misnomer.
In the case of the below image, I applied a concentric mate to the shaft of the bolt and the slot sketch point.
Then a coincident mate from under bolt head to the top of the plate.
Finally, when I attempt to lock the concentric mate rotation, this notification will come up, and I end up doing it the old way and applying a parallel mate.
I couldn't find any posts mentioning it, so here it is. The concentric mate lock does not appear to readily work in all applications.