Okay so I have found a solution if you want to recruit Minthara but you're crashing on long resting. It involves not long resting until you get to Mountain Pass. That way you skip the tiefling party or whatever cutscene you have in act 1. Long rest at Mountain Pass. The game won't crash there, then you can proceed to Moonrise Towers and find Minthara there.
It can be a bit tedious, but just respec with Withers to get most of your spell slots back.
