Dirty external root after reboot

Hi guys.

I have tp-link archer 7 v5 router running OpenWrt 19.07.1
Ext. root has been setup for that router and using config bellow:

root@a81m3:/home/sam# cat /etc/config/fstab 
config 'global'
        option  anon_swap       '0'
        option  anon_mount      '0'
        option  auto_swap       '0'
        option  auto_mount      '1'
        option  delay_root      '15'
        option  check_fs        '1'

config 'mount'
        option target           '/'
#       option device           '/dev/sda1'
        option uuid             'ac9d916a-abd2-4f53-b7c0-e021f772ed80'
        option fstype           'ext4'
        option options          'rw,noatime,nodiratime'
        option enabled          '1'
        option enabled_fsck     '1'


I removed realtime mounting option as per ext. root on USB flash and I don't want a lot of write circles on it.

So. Right now time to time (not all the time) I'm hiting dirty fs issue as soon as I software reboot that router. As results in case dirty fs detected ext root is not mounting.

even options global has "option check_fs '1'" and mount "option enabled_fsck '1'" my ext. root fs became dirty.

Why router is not checking FS before mount and how to correct this still keeping realtime option disabled?

Thank you in advance.