Hans, I have no clue either.
What we do know by now is that the DNS-handing-out-NTP-servers-pool is flauwed a lot.
As Belgium was underserved, some servers wanted to join, they got massive numbers of requests.
The DNS of the pool has major problems and need to be fixed.
See my topic. You are not the only one that asks this question.
@ask please fix the DNS problem….it’s not funny….some servers are hit real hard, others not.
See here: https://community.ntppool.org/t/i-take-a-big-hit-in-queries