Okay, pupating is when the 5th instar turns into a chrysalis. Eclosing is when the butterfly emerges from the chrysalis. And, molting is when the caterpillar sheds its skin from first through 5th instar.
There can be many causes of failure to progress. Exposure to herbicides and pesticides, bacterial, fungal, or viral infections.
Major rules to follow are fresh food, clean containers, not too much sun (indirect only), and do not place them near air conditioning vents. I have the one air conditioning vent in my dinning room blocked off.
Herndon, VA (USA)
Take care of the small things....