If we’re talking anecdotally, I am running dual stack IPv6 and have had zero issues with Minecraft or any other game on my network on Xbox, Switch, iOS and PC.
Same, my Xbox series x is noticeably faster with matchmaking games. Lobby time and searching for new games dropped from 3 minutes on average to about 45 seconds.
Minecraft does not support v6 but I wonder what caused the issues. Maybe the presence of v6 support caused DNS to give a v6 address and this caused problems? Seems unusual.