It is quite a challenge to help you as we do not know what you have migrated from to…
There was a bug when migrating from 3.x branch to 4.x already: https://forum.test.turris.cz/t/restore-raid-after-migrating-to-tos-4/11283/4. I do not know if this is still the bug or was solved, I am still having it fixed as described.
Next, original Turis had in documentation different mdadm config compare to OpenWRT I am using. Thus I am having /etc/config/mdadm configured something like:
config mdadm
option email root
list devices partitions
config array
option uuid xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx`
option device /dev/md1
option name turris:1
uuid you can examine by mdadm --examine /dev/sdd1
On the another hand you can have raid1 on btrfs level which is completely different story than…