which they should do even when they don't get a response (which they should report with "no reply", or potentially an error message they got back)
In fact, I can't shake the impression that only those probes that did _not_ get a reply, or got an error message, are the only ones reporting. And those probes that _did_ get a reply don't report it.
I understand the issue is _not_ that packets NTP aren't getting through.
Yeah, I agree with these things you said . I tried to figure out if there was something odd to Marco's responses, but got nothing. But I did run an atlas measurement to your server, using the same probe's as Marco's original meassuremnet; https://atlas.ripe.net/measurements/117694460/overview Only two did not report the results So I dunno what to make of it /giovane