When I installed grip heaters I wrapped the heating elements in electrical tape, then slid the grip back on, my throttle stuck, I pulled the grip off and removed the vast majority of the tape which was wound around the heating element on the throttle tube.. Slid the grip back on.. No more sticking..
If there is too much pressure on that tube, it will stick..
One thing that happened on my sons ACE was he dropped it when he first got it, just bent the foot brake a little but the throttle stuck, I pulled it apart lubed it reset it and it still stuck then I just made a couple adjustments to the cables at the handgrip and it worked fine. So check your cable ajustments , quick easy fix. If that doesn't work then try some of the other ideas. I wish I would have tried that first, would have saved some time!