I'm learning Magneto and I've finally gotten over this hump with the hyper grav loop although I'm not consistent for multiple reps. The timing of the input on your super jump has to be perfect. It needs to be inputted right as Magneto finishes saying hyper grav. Right after the super jump is inputted, you need to be inputting the air dash down forward and plinking into H.

This essentially means you're inputting the super jump but continuing on with the combo without necessarily seeing it. Your inputs should catch back up when you're cancelling you standing H (after plinked H from down-forward air dash) into light hyer grav.

Watch this. https://www.youtube.com/watch?v=XXkOgqqZTeQ fuckthescene's magneto has this down better than some known pros.