Error messages:
Testing existing credential for the entity: example.hostname.com has failed
Cause: Failed to execute command, error : SSH: Failed to establish SSH session to example.hostname.com
SDDC Manager 5.x
SSH host keys for the resource in question have become out of alignment with the ones stored in SDDC manager.
The SSH keys must be remediated for the individual resource that is rejecting connections using the Fix host keys script.