Why is /boot/efi filesystem on software raid md device not mounted during boot on RHEL 7.3 and 7.4?

Issue

• /boot/efi filesystem resides on a software raid md device:

# df | grep efi
/dev/md1                 204516    9668    194848   5% /boot/efi

# lsblk | grep -B1 efi
├─vda3           252:3    0  200M  0 part  
│ └─md1            9:1    0  200M  0 raid1 /boot/efi
--
├─vdb3           252:19   0  200M  0 part  
│ └─md1            9:1    0  200M  0 raid1 /boot/efi

• My system fails to mount /boot/efi filesystem during boot. The system boots successfully but /boot/efi isn't mounted after booting.