When upgrading vCenter 6.5x to version 7u3x we encountered the following problem
Following this KB
We identify the problem in the fact that we have the hostname that differs from the PNID because one is all uppercase and the other lowercase.
From the following KB we find that we can not on vCenter 6.5 updatethe hostname
To solve we proceed first with the update to the version of vcenter 6.7u3 that fixes the part of FQDN
Once updated to 6.7 relaunch the commands indicated by KB and see that the PNID and hostname coincide
Then we update to the vCenter version 7u3