[atlas] Many timeout-failures for DNS over TCP

Hi folks, I setup measurements for DNS queries over both TCP and UDP. I found the timeout and failures of TCP is far more than UDP. For example : DNS over TCP: https://atlas.ripe.net/measurements/8552847/#!probes DNS over UDP: https://atlas.ripe.net/measurements/8552846/#!probes Is it normal ? I mean is there any special timeout routine/parameters of atlas probes from normal resolver? Best regards, Davey