This sounds like the same or similar issue reported here on the forums. In addition to the problem reported here, I found that I was asked for the decryption password three times, once by grub, once to decrypt root and again to decrypt swap. The problem was resolved following the details reported in the forum post. It's unclear which package upgrade caused the problem in the first place, as far as I can tell pureos-minimal, pureos-standard, and plymouth were still present after the upgrade.