The sulfur is from the yeast getting stressed.
Possibly temperature related if your fermentation area is hot. Not neccesarily from lack of nutrients since, from what I understand, apple juice is loaded with stuff that yeast loves.
I've only ever had a sulfur smell once and that was from a batch fermenting in the garage in the middle of a heatwave in summer. Either way, the sulfur will dissipate with time, but I wouldn't bottle it till it is all gone.
Lastly, the bubbles mean nothing in terms of fermentation. They can come faster, slower or not at all in some cases. Hydrometers are cheap and really the most reliable method of measuring fermentation.