NSX Host Upgrade failed with “Unexpected Error while upgrading upgrade unit: null

I tried upgrading NSX-T 3.2.1.1.0 to 3.2.2.0.0 but failed when doing the hosts:

I was raising a case and to anyone hitting the same issue here is the final solution.

#SSH to the NSX Manager running the upgrade coordinator (master)

/etc/init.d/proton restart
/etc/init.d/upgrade-coordinator restart

# restart of proton will take a while and website will show "unhealthy"

#After a while you can run 
get cluster status

Going forward upgrade was continuing as normal.