Thank you, so I did reboot one of the host (PVE3) and re-executed the pve5to6 script, here's the output, I edited the public IP which was shown on IT (REDACTED_PUB_IP instead)
root@pve3:~# pve5to6
= CHECKING VERSION INFORMATION FOR PVE PACKAGES =
Checking for package updates..
PASS: all...