I'm amazed that those have lasted so little time. My halfords special Carrera is still going strong after years!
I am certain it's from the day I once blasted the hub area with a pressure washer and ever since the bearings have clattered as I imagine the grease was forced out by the water and as such have worn over the months. It's cone and cap secured on the Joytech hub so no matter what the bearings were gonna wear from dust/water ingress or the cap being too tight so bearings rubbing against each other with too much friction. Glad to be seeing the end of them really with a modern hub!
Just whack some grease in them? Only take 5 minutes.
I had to do that for my frame bearings, while I waited 4 weeks for them to turn up!
They've been greased already, the bearings really are on the way.