The handle is kept on with a self locking acorn nut inside the bottom of the handle. Rotating it releases the stopper (item 17 in the parts book). Look at the stopper for wear and the base of the handle to check the cam pushing it in to the swivel bracket. Make sure the kettle is all the way engaged to the gear when it locks.
Wish Star had put the drive gear on the side like Goldcrest does. so that load makes it want to stay in.