On boot cryptsetup opens one side of RAID1

[NorthVan]

I am using LUKS to encrypt my root device and that root device is actually RAID1 mdraid. Previously, genkernel (with an initrd) has managed to setup the RAID then prompt for the password.

I genkernel (4.3.16) compiled 6.6.62 (gentoo-sources) and on boot it is trying to cryptsetup one of the components of the RAID (one of the partitions that makes up the mirror), not the /dev/md126 which is the RAID device.

Kernels previous to and including 6.6.52 work fine, but I haven't recompiled one with the latest genkernel to check if it is a genkernel change that has broken things.

Another thing, after trying to open the partition with cryptsetup, this seems to cause some corruption of the EXT4 filesystem, and I have to boot from a USB and fsck before it is happy.

Any ideas how I can get back to a working setup?