Grub not trying to unlock LUKS partition

I have Ubuntu 18.04 with full disk encryption with two partitions: EFI ESP and LUKS1 encrypted root partition (no separate /boot). After installing grub and rebooting, it just shows normal grub > prompt instead of asking for LUKS password and booting Ubuntu. The kernel unlocks root filesystem by using LUKS keyfile in /etc/luks/boot_os.keyfile. Grub configuration file in /boot/efi/EFI/ubuntu/grub.cfg doesn't include cryptomount command so it's not even trying to unlock root partition:

search.fs_uuid ee03828b-76bc-4143-a2fb-f86719a90fca root cryptouuid/88251fdb112a4924a9c69892f17322e8 
set prefix=($root)'/boot/grub'
configfile $prefix/grub.cfg

If I manually edit this file adding:

cryptomount -u 88251fdb112a4924a9c69892f17322e8

as the first line, grub asks for password and system boots fine. How can I convince grub-install to include cryptomount in grub.cfg inside ESP, so that system upgrade won't break my system? ### Other config files: **/etc/default/grub**

GRUB_DEFAULT=0
GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT=1
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_DISTRIBUTOR=lsb_release -i -s 2> /dev/null || echo Debian
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""

GRUB_DISABLE_OS_PROBER=true

GRUB_ENABLE_CRYPTODISK=y
GRUB_PRELOAD_MODULES="luks cryptodisk"

**/etc/fstab**

#                
/dev/mapper/nvme0n1p2_crypt /                         ext4    errors=remount-ro  0       1
/swapfile                                 none            swap    sw                 0       0
UUID=6225-46A9  /boot/efi       vfat    defaults      0       1

**/etc/crypttab**

# 				
nvme0n1p2_crypt UUID=88251fdb-112a-4924-a9c6-9892f17322e8 /etc/luks/boot_os.keyfile luks,discard

**/etc/cryptsetup-initramfs/conf-hook**

KEYFILE_PATTERN=/etc/luks/*.keyfile

### Partitions: **lsblk -e7 -f**

NAME                FSTYPE      LABEL     UUID                                 MOUNTPOINT
sda                                                                            
├─sda1              vfat        SYSTEM    E463-AB68                            
├─sda2                                                                         
├─sda3                                                                         
└─sda4              ntfs        WinRE_DRV B27667B5766778CD                     
nvme0n1                                                                        
├─nvme0n1p1         vfat                  6225-46A9                            /boot/efi
└─nvme0n1p2         crypto_LUKS           88251fdb-112a-4924-a9c6-9892f17322e8 
  └─nvme0n1p2_crypt ext4                  ee03828b-76bc-4143-a2fb-f86719a90fca /

Also, I don't care about dual-boot right now, so I disabled OS prober in /etc/default/grub.