Measurements from Neustar/UltraDNS for some DNS servers including BIND9,They think there is weird behavior:
https://ripe85.ripe.net/wp-content/uploads/presentations/96-dknight-fewnsmanyips-ripe85-dnswg.pdf Page 8
Video: https://ripe85.ripe.net/archive/video/dave-knight_fewer-name-servers-more-addresses_main-20221027-112204.mp4 time 7:17 onwards
Measurements from Neustar/UltraDNS for some DNS servers including BIND9