Hello:
A Sotapanna has deeply experienced the four noble truths (and that is the whole point of being a stream enterer),
so he has experienced the letting go of the craving, and he knows what path lead to that letting go (so a big load of ignorance has been abandoned).
But his maturity is not enough, he doesn´t fully understand how that happened, so the hindrances come back. An Arahant regarding ignorance and craving has "its root destroyed, made like a palmyra stump, deprived of the conditions of development, not destined for future arising". He fully understands dependent origination, the four noble truths, etc. So he is liberated, no more ignorance or craving.
Regards.