Thanks.
You are right. It's the hostname things.
Also,I figured I make a typo on VM name.
Thanks a lot.
I also did a few fixes.
I found out:
the hostnames for the target names to workbench and the hostname of the ESXi Hostnames should be consistent with the ESXi hostnames when adding to vcenter.
(if FQDN is used, it should be FQDN for every ESXi hostnames entries)
Hostnames of all VMs should be in lowercases (STAF is case sensible when communicating with the VMs)
Look like it is because Workbench, STAF from Workbench, STAF to hosts and VMs are getting the hostname in different sources.