ReaR: recovery prints a WARNING !!! message when trying to rebuild the initramfs

Issue

• rear recover prints the following message after backup recovery happened

  Restore the Mountpoints (with permissions) from /var/lib/rear/recovery/mountpoint_permissions
  Running mkinitrd...
  WARNING !!!
  initramfs creation for Kernel version '<KERNEL_VERS>' failed,
  please check '/var/log/rear/rear-<HOSTNAME>.log' to see the error messages in detail
  and decide yourself, whether the system will boot or not.
  
  Running mkinitrd...
  WARNING !!!
  initramfs creation for Kernel version '3.10.0-862.3.2.el7.x86_64' failed,
  please check '/var/log/rear/rear-vm-rhel7.log' to see the error messages in detail
  and decide yourself, whether the system will boot or not.
  
  Installing GRUB2 boot loader
  Finished recovering your system. You can explore it under '/mnt/local'.