[atlas] Atlas probes not reporting NTP results on ntp0.testdns.nl ?

Dear list, If anyone knows, or is able to figure out, why most (but not all) Atlas probes don’t report results for NTP measurements to ntp0.testdns.nl, I’d appreciate your insights. Examples: https://atlas.ripe.net/measurements/116922622/ https://atlas.ripe.net/measurements/116946257/ https://atlas.ripe.net/measurements/116830921/ Ping works: https://atlas.ripe.net/measurements/116921717/ Thanks in advance. -- Marco