NTP servers debug


How can one debug the NTP requests/replies made during the startup?

I do not have my HA connected to internet.
I configured a local NTP server.
I receive the NTP requests made by HA on the NTP server side.

By some unknown reason HA continues to send NTP requests to the server and it does not finish to boot (no web interface available). As soon as I connect it to internet, it boots without any problem.