@dochy
Have you looked at : these two
https://communities.vmware.com/t5/ESXi-Discussions/NTP-Why-will-my-host-NOT-sync-time-to-the-NTP-source/td-p/2826675
https://kb.vmware.com/s/article/1005092
And this:
Please note that “An ESXi/ESX host, by default, does not accept any NTP reply with a root dispersion greater than 1.5 seconds (1500 ms).” (https://kb.vmware.com/s/article/1035833). Hence, the customer would have to add the “tos maxdist” configuration as a workaround if they want to continue using the same configured NTP servers. A flash valye of 400 can also indicate that the maximum distance threshold has been exceeded and that the tos maxdist configuration needs to be applied.