I don't know the Gem, but have had two Janomes with the auto threader.
If you move your needle ... you must put it in the default position to make the threader work.
Plus, be careful to not damage the little wire that pulls the thread thru ... and this can easily be done by trying to use the threader with the needle in the wrong position.
On my first machine with a needle threader, I could never get it to work ... til I realized that it would not, til I had it in the right needle position.
Once I clued into that ... it was slick and easy!