Trust me, there's a lockring!
Which was done up tight as, no problems. Just somehow the thread of the hub, for the sprockett, got threaded. But, when I backpedaled, it tightened back up some how!? Who knows.
Problem solved now, it's swapped to the other side and running like a dream once more.
Bloody journalists, couldn't screw a sprockett on if they tried!