OpenBSD 6.9 RAID 1C (encrypted raid1) softraid discipline can't boot

OpenBSD 6.9 RAID 1C (encrypted raid1) softraid discipline can't boot

OpenBSD 6.9 (GENERIC.MP) #473: Mon Apr 19 10:40:28 MDT 2021

one disk, shell create RAID CRYPTO, install system ok, boot ok
two disk, shell create RAID 1, install system ok, boot ok

two disk, shell create RAID 1C ok, install system ok, but boot failed in starting

boot messages:

Using drive 0, partition 3.
Loading......
probing: pc0 com0 com1 mem...
disk: hd0+ hd1+
>> OpenBSD/amd64 BOOT 3.53
open(sr0a:/etc/boot.conf): can't read disk label
boot>
cannot open sr0a:/etc/random.seed: can't read disk label
booting sr0a:/bsd: open sr0a:/bsd:can't read disk label
failed(100). will try /bsd