Comment 7 for bug 1822237

As it turns out, this was a double-whammy. The new Calamares used a cryptsetup that defaulted to luks2, which grub2 does not support. Ubiquity gets around this by using an unencrypted /boot (ewww). However, you can get cryptsetup to explicitly use one version or the other of luks rather than relying on whatever the default version is. The library used to partition, kpmcore, was modified to do exactly this. Problem fixed:

kpmcore (3.3.0-5) unstable; urgency=medium

  * Use luks1 format only

 -- Jonathan Carter <email address hidden> Sat, 06 Apr 2019 12:40:05 +0200