HS struggles with IpV6, its an ongoing issue for a number of users. There is an ongoing topic on eu forum Cant connect using mobile data [O2 UK] - #39 by TKuja-2567
and it is testified to in this post on US forum.
https://us.forums.blizzard.com/en/hearthstone/t/main-thread-t-mobile-sprint-cannot-connect-to-hearthstone-on-mobile-data/33040/240