During second phase of vCenter upgrade, following error is seen that fails the upgrade.

Error Failed to set the time via NTP
Details failed to synch to the NTP server
Code com.vmware.applmgmt.err_ntp_sync_failed
Could not setup time synchronization.
Resolution Verify that provided NTP servers are valid.

You may see following lines in logs.

/var/log/vmware/applmgmt/applmgmt.log

2019-05-28T19:29:00.964 [5784]INFO:vmware.vherd.transport.ssh_access_collector:Feature switch: VCSA_SSH_ACCESS_EVENT disabled.
2019-05-28T19:29:05.964 [5784]INFO:vmware.vherd.transport.ssh_access_collector:Feature switch: VCSA_SSH_ACCESS_EVENT disabled.
2019-05-28T19:29:10.964 [5784]INFO:vmware.vherd.transport.ssh_access_collector:Feature switch: VCSA_SSH_ACCESS_EVENT disabled.
2019-05-28T19:29:15.964 [5784]INFO:vmware.vherd.transport.ssh_access_collector:Feature switch: VCSA_SSH_ACCESS_EVENT disabled.

/var/log/vmware/ bootstrap.log

2019-05-28T18:24:11.973Z ERROR transfer_network Fatal user displayable error during upgrade network transferred.
Traceback (most recent call last):
  File "/usr/lib/vmware/cis_upgrade_runner/bootstrap_scripts/transfer_network.py", line 1218, in execute
    revertNetworkingScript)
  File "/usr/lib/vmware/cis_upgrade_runner/bootstrap_scripts/transfer_network.py", line 787, in _applyNetworking
    applyLegacyNetworking(networkConfig)
  File "/usr/lib/vmware/cis_upgrade_runner/bootstrap_scripts/apply_networking.py", line 763, in applyLegacyNetworking
    _raiseSetnetError(error)
  File "/usr/lib/vmware/cis_upgrade_runner/bootstrap_scripts/apply_networking.py", line 673, in _raiseSetnetError
    problemId=problemId)
apply_networking.UserUpgradeNetworkConfigError: [Failed to set the time via NTP. Details: Failed to sync to NTP servers.. Code: com.vmware.applmgmt.err_ntp_sync_failed, Could not set up time synchronization.]
2019-05-28T18:24:11.978Z ERROR __main__ ERROR: Fatal error during upgrade EXPORT. For more details take a look at: /var/log/vmware/upgrade/export-upgrade-runner.log
2019-05-28T18:24:11.979Z WARNING root stopping status aggregation...
2019-05-28T18:24:11.985Z INFO __main__ Merging source and destination repositories
2019-05-28T18:24:11.994Z INFO __main__ Source and destination repositories have been merged
2019-05-28T18:24:11.994Z INFO root Exiting with exit-code 1

You may see incorrect NTP connectivity.

root@vcenter [ /var/log/vmware ]# ntpq -p
remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 time.richiemcin .INIT.          16 u    -  512    0    0.000    0.000   0.000

Connectivity to any NTP server may fail.

Command> com.vmware.appliance.ntp.set --servers 211.172.242.174
Error in method: Failed to sync to NTP servers. (code
com.vmware.applmgmt.err_ntp_sync_failed)

This issue comes when source vCenter is configured with external NTP server however the configuration to destination (upgraded vCenter VM) doesn’t save correctly.

To resolve the issue follow below steps.

• Power off vCenter VM that is created as part of upgrade (Destination vCenter VM).
• Power on source vCenter VM.
• Once all vCenter services are started then go to vCenter Appliance Management Appliance (VAMI) https://vCenterIP:5480
• Select Time tab, Select Mode in Time Synchronization

• Click on Edit, select Host, click OK. Now vCenter perform time synchronization from vSphere host and similar configuration goes to destination vCenter VM during migration.

• Perform vCenter upgrade again.