my experience with galvanic corrosion and aluminum nipples (sample of 1) is that they just get stuck and it's time for new spokes and nipples. On my wheel, every spoke was stuck and you couldn't turn them. Since some of the nipples on the wheel in the OP fell apart, it sounds like they were cracking. Maybe a batch escaped heat treatment or were damaged by the wheel building machine. I always build with brass nipples now, the small amount of weight saved with aluminum doesn't make sense to me.