In s01e01, Amenadiel says to Lucifer, trying to persuade him to go back to hell:
What exactly do you think happens when the Devil leaves Hell? All of those demons, all of those tormented and tortured souls, where do you think they'd go?
In s01e07, he says more along the same lines:
Luci, since your grand departure from Hell, I've been the one that's had to patrol the gates. I've been the one keeping damned souls from slipping loose, a job, by the way, that I loathe.
Yet, in s03e07 Lucifer reveals that
all doors in Hell are open. The souls may leave anytime, but they never do because their own sense of guilt holds them there.
So why (in and out-universe) did Amenadiel give a rather different picture of what's going on while Lucifer is on his "vacation"?