Virtual machines appear in an Orphaned state in vCenter Server . VM that are running and fully functional and able to ping and RDP. vcenter shows its registered in EsxiHost-A if you login through vSphere-client that you may not able to find that vm because that vm is running in another esxi-hostB . you need to log into the each esxi host via SSH (Putty) .

To Fix the issue restart mgmt and vpxa service and   Disconnect host form VC and remove and re- add back to VC (no impact any other vm’s running in that host ).   still the same vm grayed out state ?

Finding the Esxi host on which a virtual machine is running  ?

login host via SSH   vim-cmd vmsvc/getallvms   or

escli vm process list.  with this commend you can find running virtual machine in that host.   then add back to vsphere inventory (re-register vm with the command)

vim-cmd solo/registervm /vmfs/volumes/59agedf.45aabb45893gf3f4f5f5y7874599/testvmname/testvmname.vmx 

vim-cmd solo/registervm /vmfs/volumes/datastore_name/VM_directory/VM_name.vmx

This issue may be caused by a corrupt inventory file in the ESX host. or vCenter disk full and DB full  unexpectedly stop vCenter functioning.
Hope this will be informative for you Thanks for Reading !