I don’t use luks on grub because it’s too slow to decrypt. I do know that it is almost instant on systemd-boot. It will ask for the luks password twice under certain conditions but I’m not familiar with the details. My suggestion is if you want to use luks i would install with systemd-boot which is the default on the latest ISO. You can also convert from grub to systemd-boot but i’m not the person who can guide you through that since I’m not that experienced with luks and dracut and systemd-boot setup. There is a guide to convert from grub to systemd-boot. I have used it once before trying it out but not sure if that was before dracut was introduced or whether that makes any difference. 
But i think it does.