This issue is now acknowledged in the 24.6 Known Issues bluepost
“[Added 11/8] The team is aware that some players are unable to claim the Hero Skin at the end of the Rewards Track. The issue is expected to be fixed in Patch 25.0, when players will be prompted to make their Hero Skin selection upon login. All other rewards can be claimed normally and will be automatically granted with Rewards Track swap if not claimed by that time.” – https://us.forums.blizzard.com/en/hearthstone/en/hearthstone/t/246-known-issues/97048