RAID1 (mdadm) does not start during boot

Hi there,
I have configured RAID 1 following this manual: Linux RAID mdadm [Turris wiki]
It worked well and the RAID1 is working as expected. But sometimes (about 20% of boots) the raid is not created during boot even though that mdadm service is reported to be running. If I manually restarm mdamd from terminal I get this:

root@turris:~# /etc/init.d/mdadm restart
mdadm: Fail create md0 when using /sys/module/md_mod/parameters/new_array
mdadm: /dev/md0 has been started with 2 drives.

After that RAID1 is created and can be mounted.

root@turris:~# mdadm --detail /dev/md0 
/dev/md0:
           Version : 1.2
     Creation Time : Wed Feb  1 19:39:00 2023
        Raid Level : raid1
        Array Size : 3906885440 (3725.90 GiB 4000.65 GB)
     Used Dev Size : 3906885440 (3725.90 GiB 4000.65 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Mon Feb 27 10:13:42 2023
             State : clean 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : bitmap

              Name : turris:0  (local to host turris)
              UUID : 20646394:ad410baf:6a7f66dd:f85fc211
            Events : 6464

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8        1        1      active sync   /dev/sda1

I was trying to find some error in system log and found even no mentioning of “md” related to RAID.

Is anyone else having the same problem?
Thanks for any hint!