Searching Manjaro forum for instances where someone else had same or similar problem I found this:
You haven't done it properly. Start over. Either use sudo mhwd-chroot as explained in the section Use mhwd-chroot or follow the tutorial entitled Manually Identify and Prepare the Installed Partition(s) - stop at the end of this section.
Then update the entire system: pacman -Syu
Finally, exit the chroot environment and reboot.