I haven't had time to read your other posts to figure out context for this show, so bear with me if some of this isn't relevant.
The first thing I can think of, especially if this is a community piece, is that it may be a scheduling conflict thing. Have you made sure rehearsals aren't conflicting for certain people? I know a lot of people in my community theater think its OK to miss every Thursday and every other Wednesday, plus Mondays when they'd rather be at the beach--they don't understand that the show is an every day commitment and that the quality of the final performance does, actually, rely on the volunteers.
Maybe try explaining that to them, if you haven't already. If you have, perhaps a reminder is in order.
How many crew do you need, minimum, for this show? If its a time commitment thing, you may want to sit down with each of them (all at the same time, ideally, but it sounds like that may not happen) and show them a timeline of how long you have until opening, when rehearsals are, when they would be needed, etc. and do your best to figure out which people could take nights off when-have a sort of A crew and B crew, who rotate. That way, you get to hear what their issues with being at rehearsals are, they get to see just how close the show is and hear from you how vital their role is, plus they understand that you're willing to do what you can to make it work out for everyone as well as possible.
Beyond that, what's your backup plan? Figure out who your most reliable crew members are and give them the most responsibility, train them on as much as you can, and figure out your own backup plans for running the show in case certain people don't show of a night without notice.
Did any of that help? Keep us posted as to what you end up doing!