Hi James,
Have you followed the procedure to adjust the clutch?
It should be done prior to adjusting the cable.
The cable should have slight free play when adjusted.
What happens is excessive slack develops in the clutch actuation plate.
When you pull it too far the three little ball races in the clutch actuator go too far and get stuck.
Loosen up the cable, adjust the clutch and then adjust the cable.
Follow the manual.