https://en.wikipedia.org/w/api.php?action=query&format=jsonfm&list=usercontribs&ucuser=2600:1010:B043:EC75:EFAD:9D0C:D710:2720&uclimit=500
and
https://en.wikipedia.org/w/api.php?action=query&format=jsonfm&list=usercontribs&ucuser=2600:1010:b043:ec75:efad:9d0c:d710:2720&uclimit=500
Both refer to the same IPv6 user, however the second query returns zero edits. However [[Special:Contributions]] handles both correctly